1400–50; < Latin synōnymum < Greek synṓnymon, noun use of neuter of synṓnymos synonymous; replacing Middle English sinonyme < Middle French < Latin, as above

English, with its long history of absorbing terminology from a wealth of other tongues, is a language particularly rich in synonyms —words so close in meaning that in many contexts they are interchangeable, like the nouns tongue and language in the first part of this sentence. Just about every popular dictionary defines synonym as a term having “the same or nearly the same” meaning as another, but there is an important difference between “the same” and “nearly the same.”
Noun synonyms sometimes mean exactly the same thing. A Dalmatian is a coach dog —same dog. A bureau is a chest of drawers. And if you ask for a soda on the east coast of the U.S., you’ll get the same drink that asking for a pop will get you farther west. The object referred to remains constant. But forest and wood, though often interchangeable, have different shades of meaning: a forest tends to be larger and denser than a wood. And when we move from nouns to other parts of speech, we almost always find subtle but important differences among synonyms: although the meanings overlap, they differ in emphasis and connotation. A sunset might be described equally well as beautiful or resplendent, but a beautiful baby would not usually be described as resplendent, which implies an especially dazzling appearance. The verbs make and construct mean roughly the same thing, but one is more likely to make a cake but construct a building, which is a more complex undertaking.
Lists of synonyms are useful when we are struggling to write and looking for just the right word, but each word must be considered in light of its specific definition. Notes at the bottom of a dictionary entry—especially usage notes and synonym studies—are often where we’ll find the detailed information that allows us to improve (or refine or polish ) our writing.