strong has 12 distinct synonyms spread across 7 of its 10 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 weak.
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.
having strength or power greater than average or expected
“a strong radio signal”
having or wielding force or authority
“providing the ground soldier with increasingly potent weapons”
immune to attack; incapable of being tampered with
“an impregnable fortress”
2 of the 10 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 strong.
Synonyms, antonyms and the broader and narrower relations for strong come from Princeton University’s WordNet. Full sources and licences.