c.1300, from Old French desguiser (11c.) "disguise, change one's appearance," from des- "away, off" (see dis-) + guise "style, appearance" (see guise). Originally primarily "to put out of one's usual manner" (of dress, etc.). Oldest sense preserved in phrase disguised with liquor (1560s).
It is most absurdly said, in popular language, of any man, that he is disguised in liquor; for, on the contrary, most men are disguised by sobriety. [Thomas de Quincy, "Confessions of an English Opium-Eater," 1856]Related: Disguised; disguising.
c.1400, "strange style of dress" (especially one meant to deceive), from disguise (v.).