substitute

/ˈsəb-stə-ˌtüt/

Middle English, from Anglo-French substitut, from Latin substitutus, past participle of substituere to put in place of, from sub- + statuere to set up, place

noun

  1. a person or thing that takes the place or function of another

verb

  1. to put or use in the place of another

  2. to introduce (an atom or group) as a substituent; also : to alter (something, such as a compound) by introduction of a substituent

  3. to take the place of : replace

noun

  1. a teacher who teaches a class when the usual teacher is not available