fill has 14 distinct synonyms spread across 8 of its 11 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 empty.
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.
appoint someone to (a position or a job)
a quantity sufficient to satisfy
“he ate his fill of potatoes”
Synonyms, antonyms and the broader and narrower relations for fill come from Princeton University’s WordNet. Full sources and licences.