Synonyms are words with the same or similar meanings. [...] An example of synonyms are the words begin and commence. Likewise, 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:

"a widespread impression that... Hollywood was synonymous with immorality" (Doris Kearns Goodwin)

Here are more examples of English synonyms: verb: "buy" and "purchase" adjective: "big" and "large" adverb: "quickly" and "speedily" preposition: "on" and "upon"

Note that synonyms are defined with respect to certain senses of words; for instance, pupil as the "aperture in the iris of the eye" is not synonymous with student. Likewise, he expired means the same as he died, yet my passport has expired cannot be replaced by my passport has died. [..] Some lexicographers claim that no synonyms have exactly the same meaning (in all contexts or social levels of language) because etymology, orthography, phonic qualities, ambiguous meanings, usage, etc. make them unique. Different words that are similar in meaning usually differ for a reason: feline is more formal than cat; long and extended are only synonyms in one usage and not in others (for example, a long arm is not the same as an extended arm). Synonyms are also a source of euphemisms.