substitute

One that takes the place of another; a replacement.

A word or construction used in place of another word, phrase, or clause.

To put or use (a person or thing) in place of another.

To replace (one or more atoms or groups in a compound) by other atoms or groups.

To take the place of another.

To put in the place of another; put in exchange.

To appoint; invest with delegated authority.

In chem., to replace (an atom or group) in the molecule of a compound by another atom or group. See substituent.

Put in the place or performing the functions of another; substituted.

A person put in the place of another; one acting for or in the room of another; theatrical, an understudy; specifically (military), one who for a consideration serves in an army or navy in the place of a conscript; also, a thing serving the purpose of another.