incoherent has 1 distinct synonym spread across 1 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. Its one recorded opposite is coherent.
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.
without logical or meaningful connection
“a turgid incoherent presentation”
(physics) of waves having no stable definite or stable phase relation
unable to express yourself clearly or fluently
“felt tongue-tied with embarrassment”
Synonyms, antonyms and the broader and narrower relations for incoherent come from Princeton University’s WordNet. Full sources and licences.