[n] a person or thing that takes or can take the place of another
[n] someone who takes the place of another (as when things get dangerous or difficult); "the star had a stand-in for dangerous scenes"; "we need extra employees for summer fill-ins"
[n] an athlete who plays only when another member of the team drops out
[v] put in the place of another; switch seemingly equivalent items; "the con artist replaced the original with a fake Rembrandt"; "substitute regular milk with fat-free milk"
[v] be a substitute
[v] act as a substitute for
backup, backup man, deputise, deputize, fill in, fill-in, relief, reliever, replace, replacement, reserve, stand in, stand in, stand-in, step in, sub