fill–in

a person or thing that takes the place of another I'm just a fill-in, so I have no idea where office supplies are kept Synonyms backup, cover, designated hitter, fill-in, locum tenens, pinch hitter, relief, replacement, reserve, stand-in, subRelated Words alternate, understudy; apology, makeshift, stopgap; agent, assignee, attorney, commissary, delegate, deputy, envoy, factor, procurator, proxy, rep, representative, surrogate; assistant, reliever, second; successor, superseder