expression has 15 distinct synonyms spread across 7 of its 9 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.
the feelings expressed on a person's face
“a sad expression”
expression without words
“tears are an expression of grief”
the communication (in speech or writing) of your beliefs or opinions
“expressions of good will”
a word or phrase that particular people use in particular situations
“pardon the expression”
(genetics) the process of expressing a gene
a group of words that form a constituent of a sentence and are considered as a single unit
“I concluded from his awkward constructions that he was a foreigner”
the act of forcing something out by squeezing or pressing
“the expression of milk from her breast”
Synonyms, antonyms and the broader and narrower relations for expression come from Princeton University’s WordNet. Full sources and licences.