Synonymy

Noun

1. A certain degree of similarity between the meaning(s) of several (synonymous) words or phrases. (See Usage notes below.)
2. A list or collection of synonyms, often compared and contrasted.
3. The use of synonyms to clarify or explain one's meaning.
4. The study of synonyms.
5. A system of synonyms. (The addition of quotations indicative of this usage is being sought:)