: a person or thing that takes the place of someone or something else
sports : a player who takes the place of another player during a game
: to put or use (someone or something) in place of someone or something else
: to do the job of someone else or serve the function of something else
: to replace (one person or thing) with another
What made you want to look up substitute? Please tell us where you read or heard it (including the quote, if possible).