1550s, "state or condition of being greater, superiority"(a sense now obsolete), from Middle French majorité (16c.), from Medieval Latin majoritatem (nominative majoritas) "majority," from Latin maior "greater" (see major (adj.)).
Sense of "state of being of full age, age at which the law permits a young person to manage his own affairs," is attested from 1560s. The meaning "greater number or part, more than half of the whole" (of votes, etc.) is by 1690s; that of "the excess of one of two groups of enumerated votes over the other" is by 1743. The majority "the dead" recorded from 1719; hence euphemistic verbal phrase join the majority.