understood has 2 distinct synonyms spread across 1 of its 2 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 ununderstood.
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.
fully apprehended as to purport or meaning or explanation
“the understood conditions of troop withdrawal were clear”
Synonyms, antonyms and the broader and narrower relations for understood come from Princeton University’s WordNet. Full sources and licences.