20 CFR 216.54: Who is an employee's wife or husband.

An employee's wife or husband is an individual who—

(a) Is married to the employee; and

(b) Has been married to the employee for at least one year immediately before the date the spouse applied for annuity;

(c) Is the natural parent of the employee's child;

(d) Was entitled to an annuity as a widow(er), a parent, or a disabled child under this part in the month before he or she married the employee; or

(e) Could have been entitled to a benefit listed in paragraph (d) of this section, if the spouse had applied and been old enough in the month before he or she married the employee.