ὀξύμωρον

English (LSJ)

oxymoron a witty saying, the more pointed from being paradoxical or seemingly absurd, such as insaniens sapientia, strenua inertia, splendide mendax, Serv.ad Verg.A.7.295, etc.

Wikipedia EN

An oxymoron (ὀξύμωρον, usual plural oxymorons, more rarely oxymora) is a figure of speech that juxtaposes concepts with opposing meanings within a word or phrase that creates an ostensible self-contradiction. An oxymoron can be used as a rhetorical device to illustrate a rhetorical point or to reveal a paradox. A more general meaning of "contradiction in terms" (not necessarily for rhetoric effect) is recorded by the OED for 1902.

The term is first recorded as Latinized Greek oxymōrum, in Maurus Servius Honoratus (c. AD 400); it is derived from the Greek word ὀξύς oksús "sharp, keen, pointed" and μωρός mōros "dull, stupid, foolish"; as it were, "sharp-dull", "keenly stupid", or "pointedly foolish". The word oxymoron is autological, i.e. it is itself an example of an oxymoron. The Greek compound word ὀξύμωρον oksýmōron, which would correspond to the Latin formation, does not seem to appear in any known Ancient Greek works prior to the formation of the Latin term.

Russian (Dvoretsky)

ὀξύμωρον: (ῠ) τό рит. оксиморон, до (кажущейся) нелепости заостренное выражение (образное сочетание противоречащих друг другу понятий, напр.: ἐκ γῆς ἐναυμάχουν, ἀπὸ νεῶν ἐπεζομάχουν Thuc. (лакедемоняне) вели на земле морской бой, а (афиняне) вели с кораблей бой пеший, т. е. оба войска как бы обменялись привычными для них методами боя).