substitute

n. 1 (also attrib.) Person or thing acting or used in place of another. 2 artificial alternative to a food etc. v. (-ting) (often foll. By for) (cause to) act as a substitute.  substitution n. [latin substituo -tut-]

n. One who, or that which, is substituted or put in the place of another; one who acts for another; that which stands in lieu of something else