The suffix -onym, in English and other languages, means "word, name," and words ending in -onym refer to a specified kind of name or word, most of which are classical compounds. For example, an acronym is a word formed from the initial letter or letters of each of the successive parts or major parts of a compound term (as radar). The use of -onym words provides a means of classifying, often to a fine degree of resolution, sets of nouns with common attributes.
In some words, the -onym form has been modified by replacing (or dropping) the "o". In the examples ananym and metanym, the correct forms (anonym and metonym) were pre-occupied by other meanings. Other, late 20th century examples, such as hypernym and characternym, are typically incorrectly formed neologisms for which there are more traditional words formed in -onym (hyperonym and charactonym).
The English suffix -onym is from the Ancient Greek suffix -ώνυμον (ōnymon), neuter of the suffix ώνυμος (ōnymos), having a specified kind of name, from the Greek ὄνομα (ónoma), Aeolic Greek ὄνυμα (ónyma), "name". The form -ōnymos is that taken by ónoma when it is the end component of a bahuvrihi compound, but in English its use is extended to tatpurusa compounds.
The suffix is found in many modern languages with various spellings. Examples are: Dutch synoniem, German Synonym, Portuguese sinónimo, Russian синоним (sinonim), Polish synonim, Finnish synonyymi, Indonesian sinonim.
According to a 1988 study of words ending in -onym, there are four discernible classes of -onym words: (1) historic, classic, or, for want of better terms, naturally occurring or common words; (2) scientific terminology, occurring in particular in linguistics, onomastics, etc.; (3) language games; and (4) nonce words. Older terms are known to gain new, sometimes contradictory, meanings (e.g., eponym and cryptonym). In many cases, two or more words describe the same phenomenon, but no precedence is discernable (e.g., necronym and penthonym). New words are sometimes created, the meaning of which duplicating existing terms. On occasion, new words are formed with little regard to historical principles.
Read more about -onym: Words That End in -onym