mid-14c., from Anglo-French execucioun (late 13c.), Old French execucion "a carrying out" (of an order, etc.), from Latin executionem (nominative executio) "an accomplishing," noun of action from past participle stem of exequi/exsequi "to follow out," from ex- "out" (see ex-) + sequi "follow" (see sequel).
Sense of "act of putting to death" (mid-14c.) is from Middle English legal phrases such as don execution of deth "carry out a sentence of death." Literal meaning "action of carrying something into effect" is from late 14c. John McKay, coach of the woeful Tampa Bay Buccaneers (U.S. football team), when asked by a reporter what he thought of his team's execution, replied, "I think it would be a good idea." Executor and executioner were formerly used indifferently, because both are carrying out legal orders.