Antiphrasis

Antiphrasis is the rhetorical device of saying the opposite of what is actually meant in such a way that it is obvious what the true intention is.

Some authors treat and use antiphrasis just as irony, euphemism or litotes.

When the antiphrasal use is very common, the word can become an auto-antonym, having opposite meanings depending on context. For example, Spanish dichoso originally meant "fortunate, blissful" as in tierra dichosa, "fortunate land", but it acquired the ironic and colloquial meaning of "infortunate, bothersome" as in ¡Dichosas moscas!, "Damned flies!".