-onym

Morphemes with the affix -onym are designations for either a closed set of grammatical morphemes that refer to relationships between word pairs, such as synonym and antonym; or they may stand for words of an open type that refer to a particular subject, such a toponym or characternym. By analogy they may be freely created, sometimes for no other reason than to give an erudite impression of the user who is aware that his listeners understand Greek, and thus words such as ornithonym or ichthyonym may be formed.

The first usage is of great importance in grammar. Some morphemes ending in -onym may represent words that contain components, such as house contains window, roof, and door, or they may be words so contained in others, such as steering-wheel and engine in car.
They may be generic words that stand for a class or group of equally-ranked items, such as tree for beech or elm, or belong within that class, such as lily or violet in flower.
They may have the same or similar meaning as a differently spelled word, such as sofa or couch, or they may stand in direct contrast with another, such as useful and useless.

Some morphemes have the -nym form rather than the -onym form, such as characternym, or hypernym but that may be more because of pronunciation than for etymological reasons.

Work in progress