substitute

capable of substituting in any of several positions on a team

“a utility infielder”

serving or used in place of another

“an alternative plan”

artificial and inferior

“ersatz coffee”

“substitute coffee”

a person or thing that takes or can take the place of another

an athlete who plays only when a starter on the team is replaced

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”

put in the place of another; switch seemingly equivalent items

“the con artist replaced the original with a fake Rembrandt”

“substitute regular milk for fat-free milk”

“synonyms can be interchanged without changing the context's meaning”

be a substitute

“The young teacher had to substitute for the sick colleague”

“The skim milk substitutes for cream — we are on a strict diet”

act as a substitute

“She stood in for the soprano who suffered from a cold”