1. (n.) The act of replacing.

2. (n.) The removal of an edge or an angle by one or more planes.

agency agent alternate alternative analogy backup backup man change changeling commutation comparison copy counterfeit delegation deputation deputy deputyship descendant displacement double dummy equal equivalent ersatz exchange fake fill-in ghost ghostwriter heir imitation improvement inheritor instauration locum locum tenens makeshift metaphor metonymy next best thing personnel phony pinch hitter posterity power of attorney proxy quid pro quo reactivation reconstitution reconversion redintegration reenactment reestablishment reformation rehabilitation reinstatement reinstation reinstitution reinvestiture reinvestment relief representation representative reserves restitution restoration reversion ringer second string secondary sign spares stand-in sub subrogation substituent substitute substitution succedaneum successor supersedence superseder superseding supersedure supersession supplantation supplanter supplanting supplantment surrogate switch symbol synecdoche third string tit for tat token understudy utility player vicar vicariousness vice-president vice-regent