mitre has 3 distinct synonyms spread across 3 of its 3 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.
joint that forms a corner; usually both sides are bevelled at a 45-degree angle to form a 90-degree corner
the surface of a beveled end of a piece where a miter joint is made
“he covered the miter with glue before making the joint”
Synonyms, antonyms and the broader and narrower relations for mitre come from Princeton University’s WordNet. Full sources and licences.