/ ˈsɪnənɪm; NAmE / noun
a word or expression that has the same or nearly the same meaning as another in the same language :
'Big' and 'large' are synonyms.
—compare antonym
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WORD ORIGIN
late Middle English : via Latin from Greek sunōnumon , neuter (used as a noun) of the adjective sunōnumos , from sun- with + onoma name.