Antiphrasis

·noun The use of words in a sense opposite to their proper meaning; as when a court of justice is called a court of vengeance.

antiphrasis
antĭphrăsis (better written as Gr.), is, f., = ἀντίφρασις, the use of a word in a sense opposite t...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.