Merriam-Webster Collegiate Dictionary - substitute

 I. noun  Etymology: 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 — more at statute  Date: 15th century a person or thing that takes the place or function of another  • ~ adjective  II. verb  (-tuted; -tuting)  Date: circa 1594  transitive verb  1.  a. to put or use in the place of another  b. to introduce (an atom or group) as a substituent; also to alter (as a compound) by introduction of a substituent a ~d benzene ring  2. to take the place of ; replace  intransitive verb to serve as a ~