late 14c., rendre, a legal term, "act of yielding, giving, or restoring; a return, a payment," especially of rent; see render (v.). Probably at least in part from French noun use of the infinitive.
mid-15c., "a pouring out, outflow, effusion," from out- + infinitive of pour (v.). From 1757 as "action of pouring out," probably a re-coinage, originally transferred, of things spiritual; sense of "that which is poured out" (again, usually transferred) is from 1827. A verb, outpour "to pour forth," is attested from 1670s.