tailor (n.)

"one who makes the outer garments of men and other garments of heavy stuff," late 13c., tailloir (late 12c. as a surname), from Anglo-French tailour, Old French tailleor "tailor," also "stone-mason" (13c., Modern French tailleur), literally "a cutter," from tailler "to cut," from Late Latin or old Medieval Latin taliare "to split" (compare Medieval Latin taliator vestium "a cutter of clothes"), from Latin talea "a slender stick, rod, staff; a cutting, twig."

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, 2nd ed., 1989]

The post-Latin sense development would be "piece of a plant cut for grafting," hence a verb, "cut a shoot," then, generally, "to cut." It had been connected with 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. But de Vaan (2008) writes, "There is no viable etymology for talea, unless it is a derivative of talus 'ankle, knuckle'." An Old English word for a tailor was seamere, from seam (n.).

1660s, from tailor (n.). Figurative sense of "to design (something) to suit needs" is attested from 1942. Related: Tailored; tailoring.