verb1. (often foll by for) to serve or cause to serve in place of another person or thing
2. chemistry to replace (an atom or group in a molecule) with (another atom or group)
3. logic, mathematics to replace (one expression) by (another) in the context of a third, as replacing x + y for x in 3x = k gives 3x + 3y = k
noun4. a. a person or thing that serves in place of another, such as a player in a game who takes the place of an injured colleague
b. (as modifier)
a substitute goalkeeper
Often shortened to: sub 5. grammar another name for pro-form
6. Canadian another name for supply teacher
7. nautical another word for repeater (sense 5)
8. (formerly) a person paid to replace another due for military service
▶ USAGE Substitute is sometimes wrongly used where replace is meant: he replaced (not substituted) the worn tyre with a new one