The figure of speech in which words are used in a way opposite to their normal meaning is irony. In verbal irony, a speaker’s intended meaning differs sharply from the literal meaning of the words.
For example, saying “What wonderful weather” during a storm may be ironic if the speaker intends to emphasize how unpleasant the weather is. Recognition usually depends on context, tone, or shared knowledge.
Antithesis is different: it places contrasting ideas together, often in parallel grammatical structures. Litotes uses understatement by denying the opposite, while chiasmus reverses the order of words or ideas. Anaphora repeats words at the beginnings of successive clauses.
Irony can also describe broader literary situations, such as dramatic irony, where the audience knows important information that a character does not. For this question’s definition, however, verbal irony is the precise fit.