1From a contrary position; by dint of opposition or antagonism.
Used especially of arguments reasoning from an accepted conclusion to the rejection of its contrary.
2Conversely, contrariwise; vice versa.
Late 16th century; earliest use found in Philip Stubbes (c1555–c1610), pamphleteer. From classical Latin ē contrāriō on the contrary, in contradiction, on the opposite side, inversely, on the other hand from ē out of + contrāriō, ablative of contrārius.