early 14c. as a type of men's garment, from Old French doublet
(12c.), from diminutive of duble
"double, two-fold," from Latin duplus
"twofold, twich as much" from duo
"two" (from PIE root *dwo-
"two") + -plus
"more" (see -plus
). From 1550s as "one of two things that are alike."