fortissimo 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 pianissimo.
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.
a musical composition or musical passage to be performed very loudly
a direction in music; to be played very loudly
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 fortissimo.
Synonyms, antonyms and the broader and narrower relations for fortissimo come from Princeton University’s WordNet. Full sources and licences.