From Latin 'legitimus' (lawful), from 'lex' (law) — originally about children born within lawful marriage.
Conforming to the law or to rules; able to be defended with logic or justification; born of parents lawfully married to each other.
From Medieval Latin 'lēgitimātus,' past participle of 'lēgitimāre' (to make lawful), from Latin 'lēgitimus' (lawful, according to law), from 'lēx' (law, statute). The underlying PIE root is *leǵ- (to collect, to gather). In its earliest English use, 'legitimate' referred specifically to children born within wedlock — a legal status with enormous consequences