abnormal 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 normal.
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.
departing from the normal in e.g. intelligence and development
“they were heartbroken when they learned their child was abnormal”
1 of the 3 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for abnormal.
Synonyms, antonyms and the broader and narrower relations for abnormal come from Princeton University’s WordNet. Full sources and licences.