1911 Encyclopædia Britannica/Doublet

DOUBLET (a Fr. word, diminutive of double, folded or of two thicknesses), a close-fitting garment, with or without sleeves, extending from the neck to a little below the waist, worn by men of all ranks and ages from the 14th century to the time of Charles II., when it began to be superseded by coat and waistcoat. The doublet was introduced into England from France, and was originally padded for defence or warmth. “Doublet” is also used of a pair or couple—a thing that is the facsimile of another; as in philology, one of two words differing in form, but represented by an identical root, as “alarm” or “alarum”; in optics, of a pair of lenses, combined, for example, to correct aberration. In the work of the lapidary a doublet is a counterfeit gem, made by cementing two pieces of plain glass or crystal on each side of a layer of glass (coloured to represent the stone counterfeited); a thin portion of a genuine stone may be cemented upon an inferior one, as a layer of diamond upon a topaz, or ruby on a garnet.