doublet (n.)

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."