fix has 47 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. 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.
set or place definitely
“Let's fix the date for the party!”
make infertile
“in some countries, people with genetically transmissible disabilites are sterilized”
influence an event or its outcome by illegal means
“fix a race”
informal terms for a difficult situation
“he got into a terrible fix”
1 of the 17 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 fix.
Synonyms, antonyms and the broader and narrower relations for fix come from Princeton University’s WordNet. Full sources and licences.
something craved, especially an intravenous injection of a narcotic drug
“she needed a fix of chocolate”
the act of putting something in working order again
an exemption granted after influence (e.g., money) is brought to bear
“collusion resulted in tax fixes for gamblers”
a determination of the place where something is
“he got a good fix on the target”