adequacy has 2 distinct synonyms spread across 2 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 inadequacy.
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.
the quality of being able to meet a need satisfactorily: "he questioned the adequacy of the usual sentimental interpretation of the Golden Rule"
the quality of being sufficient for the end in view
“he questioned the sufficiency of human intelligence”
Synonyms, antonyms and the broader and narrower relations for adequacy come from Princeton University’s WordNet. Full sources and licences.