antiphrasis
noun
an·tiph·ra·sis an-ˈti-frə-səs 
plural antiphrases an-ˈti-frə-ˌsēz
: the usually ironic or humorous use of words in senses opposite to the generally accepted meanings (as in "this giant of 3 feet 4 inches")
Example Sentences
Recent Examples on the Web And sometimes a name employs what the Greeks called antiphrasis. 
Washington Post, 17 Nov. 2020
Washington Post, 17 Nov. 2020 Word History
Etymology
Late Latin, from Greek, from anti- + phrasis diction — more at phrase
First Known Use
1533, in the meaning defined above