5 U.S.C. § 8441: Definitions

was married to him for at least 9 months immediately before his death; or is the mother of issue by that marriage; was married to her for at least 9 months immediately before her death; or is the father of issue by that marriage; the term “dependent”, in the case of any child, means that the employee, Member, or annuitant involved was, at the time of death of the employee, Member, or annuitant either living with or contributing to the support of such child, as determined in accordance with such regulations as the Office shall prescribe; and an unmarried dependent child under 18 years of age, including (i) an adopted child, (ii) a stepchild but only if the stepchild lived with the employee, Member, or annuitant in a regular parent-child relationship, (iii) a recognized natural child, and (iv) a child who lived with and for whom a petition of adoption was filed by an employee, Member, or annuitant and who is adopted by the widow or widower of the employee, Member, or annuitant after the death of such employee, Member, or annuitant; such unmarried dependent child regardless of age who is incapable of self-support because of mental or physical disability incurred before age 18; or such unmarried dependent child between 18 and 22 years of age who is a student regularly pursuing a full-time course of study or training in residence in a high school, trade school, technical or vocational institute, junior college, college, university, or comparable recognized educational institution.