contra-

"against, over against, opposite, on the opposite side; on the contrary, contrariwise," mid-14c., from Latin contra (prep. and adv.) "against," originally "in comparison with," ablative singular feminine of *com-teros, from Old Latin com "with, together" (see com-) + -tr, zero-degree form of the comparative suffix -ter-.

1570s, probably from a dialectal survival of Old English wiðer "against, contrary, opposite" (see with) + plural suffix. Usually said to be so called because the withers are the parts of the animal that oppose the load. Compare German Widerrist "withers," from wider "against" + Rist "wrist."