What is the X in X-mas?
late 15c. (implied in applauding), "to express agreement or approval; to praise," from Latin applaudere "to clap the hands in approbation, to approve by clapping hands; to strike upon, beat," from ad "to" (see ad-) + plaudere "to clap" (see plaudit). Sense of "express approval of" is from 1590s; that of "to clap the hands" is from 1590s. Figurative sense arrived in English before literal. Related: Applauded; applauding.