1. (v. t. & i.) To study, as another actor's part, in order to be his substitute in an emergency; to study another actor's part.

2. (n.) One who studies another's part with a view to assuming it in an emergency.

act for advocate agent alter ego alternate alternative amicus curiae analogy answer for appear for attorney back up backup backup man bit player champion change change places with changeling commission comparison copy counterfeit crowd out cut out deputize deputy displace double double for dummy equal equivalent ersatz exchange executive officer exponent extra fake figurant figurante figurehead fill in for fill-in front for ghost ghostwrite ghostwriter imitation lieutenant locum locum tenens makeshift metaphor metonymy mute next best thing paranymph personnel phony pinch hitter pinch-hit pinch-hit for pleader procurator proxy relief relieve replace replacement represent representative reserve reserves ringer second second in command second string secondary sign spares speak for spear-carrier spell spell off stand in for stand-in standby sub subrogate substituent substitute substitute for substitution succedaneum succeed supe super supernumerary supersede superseder supplant supplanter support supporting actor supporting cast surrogate swap places with symbol synecdoche third string token understudy for utility man utility player vicar vicar general vice vice-president vice-regent vicegerent walk-on walking gentleman