bad has 16 distinct synonyms spread across 12 of its 17 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 good.
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.
with great intensity (`bad' is a nonstandard variant for `badly')
“the injury hurt badly”
that which is below standard or expectations as of ethics or decency
“take the bad with the good”
4 of the 17 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for bad.
Synonyms, antonyms and the broader and narrower relations for bad come from Princeton University’s WordNet. Full sources and licences.