synonymy; synonymity
Technical term used in linguistics and computing to describe the relationship between words with the same or nearly the same meaning.
Synonymy is an important concept in natural language processing.
この二つの語の同義性について議論する。
We discuss the synonymy of these two words.
同義語 is a synonym (a word), whereas 同義性 is the state or quality of synonymy.
Compound of 同義 (dōgi, 'same meaning') + 性 (-sei, '-ness, property'). The exact historical derivation is uncertain, but the word follows a common pattern for forming abstract nouns in modern technical Japanese.