mid-14c., "type of tight-fitting men's outer garment covering the body from the neck to the hips or thighs," from Old French doublet (12c.), from diminutive of duble "double, two-fold," from Latin duplus "twofold, twice as much" (see double (adj.)).
Up until 18c. doublet and hose meant "typical male attire." From 1550s as "one of two things that are alike."