Dictionary.net

A Latin prefix, signifying against or in opposition; opposite, lower, applied to alto and tenor, when they form the lowest part in the harmony.

On the other hand; on the contrary; opposite; a common prefix, with its form counter, signifying against; in opposition.

A prefix from the Lat, contra, against, in opposition; used in compound words.

prep. [Latin] Against; —a prefix to many words, giving the sense of opposition or contrast.

A Latin preposition, used in composition, which signifies, against.