"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-.
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Definitions of Contras from WordNet
a Nicaraguan counterrevolutionary guerrilla force from 1979 to 1990; it opposed a left-wing government, with support from the United States;