Synonyms

Synonyms are different words witsh identical or very similar meaning. Words that are synonyms said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn (σύν) ("with") and onoma (ὄνομα) ("name"). The words car and automobile are synonyms. Similarly, if we talk about a long time or an extended time, long and extended become synonyms. In the figurative sense, two words are often said to be synonymous if they have the same connotation.
http://en.wikipedia.org/wiki/Synonym