(1):

(subj. 3d pers. sing.) Let it stand; - a word used by proof readers to signify that something once erased, or marked for omission, is to remain.

(2):

(v. t.) To cause or direct to remain after having been marked for omission; to mark with the word stet, or with a series of dots below or beside the matter; as, the proof reader stetted a deled footnote.