language has 12 distinct synonyms spread across 6 of its 6 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.
a systematic means of communicating by the use of sounds or conventional symbols
“he taught foreign languages”
(language) communication by word of mouth
“his speech was garbled”
the text of a popular song or musical-comedy number
“his compositions always started with the lyrics”
the cognitive processes involved in producing and understanding linguistic communication
“he didn't have the language to express his feelings”
a system of words used to name things in a particular discipline
“legal terminology”
Synonyms, antonyms and the broader and narrower relations for language come from Princeton University’s WordNet. Full sources and licences.