Con"tra*ries (? ∨ ; 48), n. pl. [Pl. of Contrary, n.] Logic
Propositions which directly and destructively contradict each other, but of which the falsehood of one does not establish the truth of the other.
If two universals differ in quality, they are contraries; as, every vine is a tree; no vine is a tree. These can never be both true together; but they may be both false.
© Webster 1913.