intercession n.

early 15c., "act of interceding;" c. 1500, "intercessory prayer, a pleading on behalf of oneself or another," from Latin intercessionem (nominative intercessio) "a going between, coming between, mediation," noun of action from past participle stem of intercedere "intervene, come between, be between" (in Medieval Latin "to interpose on someone's behalf;" see intercede). The sense "pleading on behalf of another" developed in Christianity.