For example, referring to a 7 feet tall, 450 lb man with the nickname "Tiny".
(From the online OED) Antiphrasis (Rhetoric)
- A figure of speech by which words are used in a sense opposite to their proper meaning.
1533 T. More Debellacyon Salem & Bizance i. v. f. xxix, The fygure of ironye or antiphrasys.
1589 G. Puttenham Arte Eng. Poesie iii. xviii. 159 Antiphrasis, or the Broad floute..as..to [say to] a Negro..in good sooth ye are a faire one.
1650 O. Cromwell Lett. & Speeches (Carlyle) (1857) ii. 110 You are pastors, but it is by an antiphrasis, a minime pascendo.
1739 tr. C. Rollin Anc. Hist. (ed. 2) VIII. 15 He was, by antiphrasis, sirnamed Philopator.
1853 E. K. Kane U.S. Grinnell Exped. (1856) iv. 33 It was a bold antiphrasis that gave such a vernal title [Greenland] to this birth-place of icebergs.
the term is antiphrasis from the Greek antiphrazein, “to express by antithesis or negation”.Please see:http://rhetoric.byu.edu/figures/A/antiphrasis.htm