v. 1 Sometimes, substitute for. replace, exchange, displace, relieve, supplant; switch; take the place of, stand in for, double for, Colloq sub for, cover for, swap or swop, US and Canadian pinch-hit for She substituted the real diamond with a paste replica I will substitute for you while you are away.
n. 2 substitution, replacement, alternative, relief, representative, deputy, delegate, stand-in, stand-by, understudy, surrogate, succedaneum, Brit locum (tenens), US and Canadian alternate In those days a man could hire a substitute to serve in his place in the militia