mountain four o'clock has 1 distinct synonym spread across 1 of its 1 sense. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
leafy wildflower with lavender-pink flowers that open in the evening and remain through cool part of the next day; found in open woods or brush in mountains of southern Colorado to Arizona and into Mexico
Synonyms, antonyms and the broader and narrower relations for mountain four o'clock come from Princeton University’s WordNet. Full sources and licences.