What is the X in X-mas?
1610s, "loose outer garment" (worn by men in Eastern countries or in ancient times), from French veste, from Italian vesta, veste "robe, gown," from Latin vestis, from vestire "to clothe" (see vest (v.)). The sleeveless garment worn by men beneath the coat was introduced by Charles II.
The King hath yesterday, in Council, declared his resolution of setting a fashion for clothes .... It will be a vest, I know not well how; but it is to teach the nobility thrift. [Pepys, "Diary," Oct. 8, 1666]
A computer search tool (1990s+ Computer)