red cedar has 9 distinct synonyms spread across 3 of its 4 senses. 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.
large valuable arborvitae of northwestern United States
small juniper found east of Rocky Mountains having a conic crown, brown bark that peels in shreds, and small sharp needles
tall tree of the Pacific coast of North America having foliage like cypress and cinnamon-red bark
fragrant reddish wood of any of various red cedar trees
Synonyms, antonyms and the broader and narrower relations for red cedar come from Princeton University’s WordNet. Full sources and licences.