Contra

Preposition

 * 1) against; contrary or opposed to

Adverb

 * 1) to the contrary to something

Noun

 * 1)  a deal to swap goods or services
 * 2)  an entry that cancels another entry
 * 3)  any of the musical instruments in the contrabass range, e.g. contrabassoon, contrabass clarinet or, especially, double bass

Thesaurus
a rebours, adverse to, against, against the grain, against the tide, against the wind, antipode, antipodes, antipole, antithesis, antonym, arsy-varsy, at cross-purposes, at cross-purposes with, at daggers, at daggers drawn, at issue, at odds, at variance, at war with, athwart, by contraries, con, contradictory, contrarily, contrariously, contrariwise, contrary, contrawise, converse, conversely, counter, counter to, counterbalance, countercheck, counterpoint, counterpoise, counterpole, counterterm, cross, dead against, eyeball-to-eyeball, facing, foil, fronting, in conflict with, in confrontation, in flat opposition, in hostile array, in opposition, in opposition to, inverse, inversely, just the opposite, nay rather, obverse, offset, on the contrary, opposed to, opposite, opposite number, oppositely, otherwise, over, per contra, quite the contrary, rather, reverse, setoff, the contrary, the other side, to the contrary, topsy-turvy, tout au contraire, toward, up in arms, upside down, versus, vice versa, vis-a-vis, with crossed bayonets