rigid has 6 distinct synonyms spread across 4 of its 5 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 nonrigid.
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.
incapable of compromise or flexibility
incapable of adapting or changing to meet circumstances
“a rigid disciplinarian”
designating an airship or dirigible having a form maintained by a stiff unyielding frame or structure
Synonyms, antonyms and the broader and narrower relations for rigid come from Princeton University’s WordNet. Full sources and licences.