c. 1600, "action of excreting;" 1620s, "that which is excreted," from French excrétion (16c.), from Latin excretionem (nominative excretio), noun of action from past-participle stem of excernere "to sift out, separate" (see excrement).

"to throw out or eliminate," specifically "to eliminate from an body by a process of secretion and discharge," 1610s, from Latin excretus, past participle of excernere "to sift out, discharge," from ex "out" (see ex-) + cernere "sift, separate" (from PIE root *krei- "to sieve," thus "discriminate, distinguish"). Related: Excreted; excreting.