1 rare The action of showing by one's own words or behaviour that one is guilty of a crime or error; self-condemnation; an instance of this.
2Strong belief proceeding from one's own knowledge or experience; confidence in one's own abilities, judgement, opinions, etc.
Also occasionally as a count noun.
Early 17th century; earliest use found in Dialogue Cosmophilus & Theophilus. From self- + conviction.