古フランス語のtailleor「仕立てる」から、tailler「切る」から、ラテン語のtaliare「切り離す、切る」から、talea「切る、小枝、芽」から、語源的にはtally「小売」と同じ。
Although historically the tailor is the cutter, in the trade the 'tailor' is the man who sews or makes up what the 'cutter' has shaped. [OED]The post-Latin sense development would be "piece of a plant cut for grafting," hence a verb, "cut a shoot," then, generally, "to cut." Possible cognates include Sanskrit talah "wine palm," Old Lithuanian talokas "a young girl," Greek talis "a marriageable girl" (for sense, compare slip of a girl, twiggy), Etruscan Tholna, name of the goddess of youth.
Kent. ... You cowardly rascal, nature disclaims in thee; a tailor made thee.One who makes outer garments to order, as opposed to a clothier, who makes them for sale ready-made. Tailor-made first recorded 1832 (in a figurative sense); literal sense was "heavy and plain, with attention to exact fit and with little ornamentation," as of women's garments made by a tailor rather than a dress-maker.
Corn. Thou art a strange fellow: a tailor make a man?
Kent. Ay, a tailor, sir: a stone cutter, or a painter, could not have made him so ill, though they had been but two hours at the trade.
["King Lear"]