Synonym‏ [Noun.]

‘Two or more words with very closely related meanings are called synonyms. […] We should keep in mind that the idea of “sameness” of meaning used in discussing synonymy is not necessarily “total sameness.” There are many occasions when one word is appropriate in a sentence, but its synonym would be odd.”

– Yule, G. 1985. The Study of Language Cambridge, United Kingdom: Cambridge University Press (2010) p. 117