1530s, "mutually opposed, at variance, inconsistent, incapable of being true together," from Late Latin contradictorius "containing a contradiction or objection," from contradictus, past participle of contradicere "to speak against" (see contradiction).
Sense of "denying that something stated or approved is completely true" is from c. 1600. Meaning "fond of contradicting" is from 1891. Other adjectives, now obsolete, in the same sense were contradictorious (early 15c.), contradictious (c. 1600), contradictive (1620s). Related: Contradictorily. Used earlier as a noun (late 14c.) in plural contradictories, "a pair of propositions inconsistent with each other."