mid-14c., "associate, fellow, comrade;" late 14c.,"habitual companion, friend;" from Middle Low German mate, gemate "one eating at the same table, messmate," from Proto-Germanic *ga-matjon, meaning "(one) having food (*matiz) together (*ga-)." For *matiz, see meat. It is built on the same notion as companion (which is thought to be a loan-translation from Germanic). Cognate with German Maat "mate," Dutch maat "partner, colleague, friend."
Meaning "one of a wedded pair" is attested from 1540s. Used as a form of address by sailors, laborers, etc., at least since mid-15c. Meaning "officer on a merchant vessel" is from late 15c.; his duty is to oversee the execution of the orders of the master or commander.
c. 1500, transitive, "to equal, rival," 1590s as "to match as mates, couple, join in marriage," from mate (n.1). Also, of animals, "to pair for the purpose of breeding" (c. 1600). Intransitive sense of "be joined in companionship" is from 1580s. Related: Mated; mating.
"to checkmate," c. 1300, from Old French mater "to checkmate, defeat, overcome," from mat "checkmated" (see checkmate (v.)).
in chess, "a condition of checkmate, the state of the king when he is in check and cannot move out of it," c. 1300, mat, from Old French mat, from mater "to checkmate" (see mate (v.2)).
Fool's mate, a mode of checkmate in which the tyro, moving first, is mated by his opponent's second move.—Scholar's mate, a simple mode of checkmate, sometimes practised on inexperienced players, in which the skilled player's queen, supported by a bishop, mates the tyro in four moves. [Century Dictionary]