mid-15c., "lawfully begotten, born of parents legally married," from past participle of Old French legitimer and directly from Medieval Latin legitimatus, past participle of legitimare "make lawful, declare to be lawful," from Latin legitimus "lawful," originally "fixed by law, in line with the law," from lex (genitive legis) "law" (see legal). Transferred sense of "genuine, real" is attested from 1550s. Related: Legitimately; legitimateness. The older adjective in English was legitime "lawful, of legitimate birth" (late 14c.), from Old French legitime, from Latin legitimus.

mid-15c., legitimacion, "official declaration of legitimacy," from Old French légitimation and directly from Medieval Latin legitimationem (nominative legitimatio), noun of action from past-participle stem of legitimare "make lawful, declare to be lawful" (see legitimate (adj.)).

1795, from Latin legitimus "lawful" (see legitimate (adj.)) + -ize. Earlier were legitimatize (1791), legitimate (1590s). Related: Legitimized; legitimizing; legitimization.

"establish the legitimacy of, make lawful," 1590s, from Medieval Latin legitimatus, past participle of legitimare "make lawful" (see legitimate (adj.)). Related: Legitimated; legitimating.

"insistence upon legitimacy," 1849, from French légitimisme (1834); see legitimate (adj.) + -ism. In 19c. especially with reference to French or Spanish politics and conservative adherence to "legitimate" claimants to the throne.

1841, from French légitimiste (1830), from légitime "legitimate," from legitimer (see legitimate (adj.)). A supporter of "legitimate" authority, in France, after 1830, especially of supporters of the elder Bourbon line (in opposition to that of the Orleans family).

"state of being legitimate" in any sense, 1690s of children, 1812 of kings and governments, general use by 1836; see legitimate (adj.) + -cy. Legitimateness (1610s) is an earlier word for it. Middle English had legitimation (mid-15c.).