substitution (n.)

late 14c., "appointment of a subordinate or successor," from Middle French substitution or directly from Late Latin substitutionem (nominative substitutio) "a putting in place of (another)," noun of action from past participle stem of Latin substituere "put in place of another, place under or next to, present, submit," from sub "under" (see sub-) + statuere "set up," from PIE root *sta- "to stand, make or be firm," with derivatives meaning "place or thing that is standing."