From the Greek for "together" & "name", it means having the same meaning
[DOC] [TLE] Synonym dictionary definition | synonym defined [PAR] a word having the same or nearly the same meaning in one or more senses as 
another ... Greek syn?nymon, of like meaning or like name ; from syn-, together +
... [DOC] [TLE] Word Root Of The Day: onym | Membean [PAR] nameonym: nameanonymouspseudonymeponymsynonymantonymacronym ...