"expression or round of applause, praise bestowed with audible demonstrations," 1620s, short for plaudite "an actor's request for applause" (1560s), from Latin plaudite! "applaud!" second person plural present imperative of plaudere "to clap, strike, beat; applaud, clap the hands; approve," a word of unknown origin (also in applaud, explode). This was the customary appeal for applause that Roman actors made at the end of a play. In English, the -e went silent then was dropped. Related: Plauditor; plauditory.
word-forming element making adjectives from verbs, meaning "pertaining to, tending to; doing, serving to do," in some cases from Old French -if, but usually directly from Latin adjectival suffix -ivus (source also of Italian and Spanish -ivo). In some words borrowed from French at an early date it has been reduced to -y (as in hasty, tardy).