Definition of "Substitute" :

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

noun: someone who takes the place of another (as when things get dangerous or difficult)

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

verb: put in the place of another; switch seemingly equivalent items

"Substitute regular milk for fat-free milk."

verb: be a substitute

"The young teacher had to substitute for the sick colleague."

verb: act as a substitute

adjective: artificial and inferior

"Substitute coffee."

adjective: serving or used in place of another

adjective: capable of substituting in any of several positions on a team