1711, "comparison by exhibiting the dissimilar or contrary qualities in the things compared," from contrast (v.). From 1764 as "that which shows striking difference from another when compared to it," also "opposition in respect of certain qualities."
1540s, "contrary to nature, reason, or common sense," from Latin praeposterus "absurd, contrary to nature, inverted, perverted, in reverse order," literally "before-behind" (compare topsy-turvy,cart before the horse), from prae "before" (see pre-) + posterus "subsequent, coming after," from post "after" (see post-).
The sense gradually shaded into "foolish, ridiculous, stupid, absurd." The literal meaning "reversed in order or arrangement, having that last which ought to be first" (1550s) is now obsolete in English. In 17c. English also had a verb preposterate "to make preposterous, pervert, invert." Related: Preposterously; preposterousness.
"to revoke (a command or order)," early 15c., contremaunden, from Anglo-French and Old French contremander "reverse an order or command" (13c.), from contre- "against" (see contra (prep., adv.)) + mander, from Latin mandare "to order" (see mandate (n.)). Related: Countermanded; countermanding. As a noun, "a contrary order," 1540s.
1630s, "completely, in an extreme degree" (with opposed, contrary, etc.), from diametrical (see diametric + -al (1)) + -ly (2). Originally and mostly in figurative use: the two points that mark the ends of a line of diameter are opposite one another. Diametrical opposition translates Aristotle's phrase for "extreme opposition."