delivered the opinion of the Court.
In this case we review a determination by petitioner, the Secretary of Health and Human Services, that “child’s insurance benefits” paid pursuant to Title II of the Social Security Act, see 49 Stat. 623, as amended, 42 U. S. C § 402(d) (1982 ed. and Supp. V), do not constitute “child support” as that term is used in a provision in Title IV of the Act governing eligibility for Aid to Families With Dependent Children (AFDC). See 42 U. S. C. §602(a)(8)(A)(vi) (1982 ed., Supp. V). We uphold the Secretary’s determination and reverse *480the contrary holding of the United States Court of Appeals for the Fourth Circuit.
Title IV requires the applicable agencies of States participating in the AFDC program to consider “other income and resources of any child or relative claiming” AFDC benefits “in determining need” for benefits. § 602(a)(7)(A). The state agencies “shall determine ineligible for aid any family the combined value of whose resources . . . exceeds” the level specified in the Act. § 602(a)(7)(B). Central to this case is one of the amendments to Title IV in the Deficit Reduction Act of 1984 (DEFRA), Pub. L. 98-369, §2640, 98 Stat. 1146-1146, affecting eligibility for AFDC benefits. This amendment provides:
“. . . [W]ith respect to any month, in making the determination under [§ 602(a)(7)], the State agency—
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“shall disregard the first $50 of any child support payments received in such month with respect to the dependent child or children in any family applying for or receiving aid to families with dependent children (including support payments collected and paid to the family under section 657(b) of this title). . . .” 42 U. S. C. § 602(a)(8)(A)(vi) (1982 ed., Supp. V) (emphasis added).
The Secretary has declined to “disregard” under this provision the first $50 of Title II Social Security child’s insurance benefits paid on behalf of children who are members of families applying for AFDC benefits. In the Secretary’s view, the Government-funded child’s insurance benefits are not “child support” for purposes of § 602(a)(8)(A)(vi) because that term, as used throughout Title IV, “invariably refers to payments from absent parents.” Brief for Petitioner 13.
Respondents are custodial parents receiving AFDC benefits who are aggrieved by the implementation of the DEFRA amendments. They sued in the United States District Court for the Eastern District of Virginia challenging petitioner’s interpretation of the disregard on statutory and constitu*481tional grounds. See Complaint, App. 31-33. The District Court granted summary judgment for respondents on the basis of their statutory challenge and thereby avoided reaching the constitutional challenge. App. to Pet. for Cert. 22a.
The United States Court of Appeals for the Fourth Circuit affirmed the District Court. Stroop v. Bowen, 870 F. 2d 969, 975 (1989). According to the Court of Appeals, Congress nowhere explicated its use of the term “child support” in § 602(a)(8)(A)(vi) and the only known discussion of the purpose of the disregard provision is in our decision in Bowen v. Gilliard, 483 U. S. 587 (1987). As read by the Court of Appeals, Bowen noted that “the disregard of the first $50 paid by a father serves to mitigate the burden of the changes wrought by the DEFRA amendments.” 870 F. 2d, at 974 (citing 483 U. S., at 594). The court reasoned that although we had not considered the question of Title II child’s insurance payments in Bowen, the disregarding of the first $50 of such payments, “received in lieu of payments made by a father,” would serve the same purpose of mitigating the harshness of the DEFRA amendments. 870 F. 2d, at 974. Since AFDC applicants receiving Title II child’s insurance benefits are burdened by the DEFRA amendments no less than applicants receiving payments directly from noncustodial parents, no rational basis exists for according one class of families the mitigating benefit of the disregard while depriving another indistinguishable class of families of the same benefit. The court thus rejected the Secretary’s interpretation of the disregard and added that to construe § 602(a)(8)(A)(vi) to exclude the Title II benefits from the disregard would raise constitutional equal protection concerns. Id., at 975. We granted certiorari, 493 U. S. 1018 (1990), to resolve the conflict between the decision of the Fourth Circuit and the contrary holding of the Court of Appeals for the Eighth Circuit in Todd v. Norman, 840 F. 2d 608 (1988).
We think the Secretary’s construction is amply supported by the text of the statute which shows that Congress used *482“child support” throughout Title IV of the Social Security Act and its amendments as a term of art referring exclusively to payments from absent parents. This being the case, we need go no further:
“'If the statute is clear and unambiguous “that is the end of the matter, for the court, as well as the agency, must give effect to the unambiguously expressed intent of Congress.” ... In ascertaining the plain meaning of the statute, the court must look to the particular statutory language at issue, as well as the language and design of the statute as a whole.’” K mart Corp. v. Cartier, Inc., 486 U. S. 281, 291-292 (1988) (internal citations omitted).
As an initial matter, the common usage of “child support” refers to legally compulsory payments made by parents. Black’s Law Dictionary 217 (5th ed. 1979) defines “child support” as
“[t]he legal obligation of parents to contribute to the economic maintenance, including education, of their children; enforceable in both civil and criminal contexts. In a dissolution or custody action, money paid by one parent to another toward the expenses of children of the marriage.”
Attorneys who have practiced in the area of domestic relations law will immediately recognize this definition. Respondents insist, however, that we have traditionally “turned to authorities of general reference, not to legal dictionaries, to [give] ‘ordinary meaning to ordinary words.’” Brief for Respondents 20 (citing Sullivan v. Everhart, 494 U. S. 83, 91-92 (1990)). But the general reference work upon which respondents principally rely defines “child support” as “money paid for the care of one’s minor child, especially] payments to a divorced spouse or a guardian under a decree of divorce.” Random House Dictionary of the English Language 358 (2d ed. 1987) (emphasis added) (cited at Brief for Respondents 20). Respondents also seek to bolster their view *483with definitions of the word “support” from other dictionaries. Ibid. But where a phrase in a statute appears to have become a term of art, as is the case with “child support” in Title IV, any attempt to break down the term into its constituent words is not apt to illuminate its meaning.
Congress’ use of “child support” throughout Title IV shows no intent to depart from common usage. As previously noted, the provisions governing eligibility for AFDC benefits, including the “disregard” provision in issue here, are contained in Title IV of the Social Security Act. 42 U. S. C. §§601-679a (1982 ed. and Supp. V). Title IV, as its heading discloses, establishes a unified program of grants “For Aid and Services to Needy Families With Children and For Child-Welfare Services” to be implemented through cooperative efforts of the States and the Federal Government. Part D of Title IV is devoted exclusively to “Child Support and Establishment of Paternity.” See §§651-667. The first provision in Part D authorizes appropriations
“[f]or the purpose of enforcing the support obligations owed by absent parents to their children and the spouse (or former spouse) with whom such children are living, [and] locating absent parents . . . .” 42 U. S.C. §651 (1982 ed., Supp. V) (emphasis added).
The remainder of Part D, 42 U. S. C. §§652-667 (1982 ed. and Supp. V), abounds with references to “child support” in the context of compulsory support funds from absent parents. See, e. g., §§ 652(a)(1), 652(a)(7), 652(a)(10)(B), 652(a)(10)(C), 652(b), 653(c)(1), 654, 654(6), 654(19)(A), 654(19)(B), 656(b), 657(a), 659(a), 659(b), 659(d), 661(b)(3), 662(b). Section 653, indeed, creates an absent parent “Locator Service.”
The statute also makes plain that Congress meant for the Part D Child Support program to work in tandem with the AFDC program which constitutes Part A of Title IV, §§601-615. Section 602(a)(27) requires state plans for AFDC participation to “provide that the State has in effect a *484plan approved under part D . . . and operates a child support program in substantial compliance with such plan.” Section 602(a)(26) requires State AFDC plans to
“provide that, as a condition of eligibility for [AFDC benefits], each applicant or recipient will be required—
“(A) to assign the State any rights to support from any other person such applicant may have (i) in his own behalf or in behalf of any other family member for whom the applicant is applying for or receiving aid, . . . [and]
“(B) to cooperate with the State . . . (ii) in obtaining support payments for such applicant and for a child with respect to whom such aid is claimed . . .
Part D, in turn, requires state plans implementing Title IV Child Support programs to
“provide that (A) in any case in which support payments are collected for an individual with respect to whom an assignment under section 602(a)(26) [in Part A] of this title is effective, such payments shall be made to the State for distribution pursuant to section 657 [in Part D] of this title . . . §654(5).
These cross-references illustrate Congress’ intent that the AFDC and Child Support programs operate together closely to provide uniform levels of support for children of equal need. That intent leads to the further conclusion that Congress used the term “child support” in § 602(a)(8)(A)(vi), and in Part A generally, in the limited sense given the term by its repeated use in Part D. The substantial relation between the two programs presents a classic case for application of the “normal rule of statutory construction that ‘ “identical words used in different parts of the same act are intended to have the same meaning.””’ Sorenson v. Secretary of Treasury, 475 U. S. 851, 860 (1986) (quoting Helvering v. Stockholms Enskilda Bank, 293 U. S. 84, 87 (1934) (in turn quoting Atlantic Cleaners & Dyers, Inc. v. United States, 286 U. S. 427, 433 (1932))).
*485Since the Secretary’s interpretation of the § 602(a)(8)(A) (vi) disregard incorporates the definition of “child support” that we find plain on the face of the statute, our statutory inquiry is at an end. The disregard, accordingly, does not admit of the interpretation advanced by respondents and accepted by both courts below. Though Title II child’s insurance benefits might be characterized as “support” in the generic sense, they are not the sort of child support payments from absent parents envisioned in the Title IV scheme. The Title II payments are explicitly characterized in § 402(d) as “insurance” benefits and are paid out of the public treasury to all applicants meeting the statutory criteria. Thus no portion of any § 402(d) payments may be disregarded under § 602(a)(8)(A)(vi).
The Court of Appeals construed the statute the way it did in part because it felt the construction we adopt would raise a serious doubt as to its constitutionality. App. to Pet. for Cert. 12a. We do not share that doubt. We agree with the Secretary that Congress’ desire to encourage the making of child support payments by absent parents, see, e. g., 42 U. S. C. §§602(a)(26)(B)(ii) and 654(5) (1982 ed., Supp. V) (requiring APDC recipients to assist in the collection of child support payments for distribution by the States under Part D)), affords a rational basis for applying the disregard to payments from absent parents, but not to Title II insurance payments which are funded by the Government. This sort of statutory distinction does not violate the Equal Protection Clause “if any state of facts reasonably may be conceived to justify it.” Bowen v. Gilliard, 483 U. S., at 601.
The judgment of the Court of Appeals is therefore
Reversed.