synonym (n.)

"word having the same sense as another," early 15c. (but usually in plural form before 18c., or, if singular, as synonyma), from Old French synonyme (12c.) and directly from Late Latin synonymum, from Greek synonymon "word having the same sense as another," noun use of neuter of synonymos "having the same name as, synonymous," from syn- "together, same" (see syn-) + onyma, Aeolic dialectal form of onoma "name" (from PIE root *no-men- "name").