faint has 18 distinct synonyms spread across 7 of its 8 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
deficient in magnitude; barely perceptible; lacking clarity or brightness or loudness etc
“a faint outline”
weak and likely to lose consciousness
“suddenly felt faint from the pain”
lacking conviction or boldness or courage
“faint heart ne'er won fair lady”
a spontaneous loss of consciousness caused by insufficient blood to the brain
1 of the 8 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 faint.
Synonyms, antonyms and the broader and narrower relations for faint come from Princeton University’s WordNet. Full sources and licences.