omission n.

mid-14c., omissioun, "a neglect or failure to do what one has power to do or ought to do," from Anglo-French omission (early 14c.), Old French omission and directly from Late Latin omissionem (nominative omissio) "an omitting," noun of action from past-participle stem of Latin omittere "disregard," literally "let go, let fall" (see omit). Meaning "act of leaving out" is from 1550s. Related: Omissible.