Longman Dictionary of Contemporary English
contra-
prefix
EXAMPLES FROM OTHER ENTRIES
▪ to contravene something
Douglas Harper's Etymology Dictionary
contra-
word-forming element meaning "against, in opposition," from Latin adverb and preposition contra (see contra). The Latin word was used as a prefix in Late Latin. In French, it became contre- and passed into English as counter-. The Old English equivalent was wiðer (surviving in withers and widdershins), from wið "with, against."
Wiktionary
contra-
pre. against