First Known Use of synonym 15th century, in the meaning defined at sense 1

First Known Use of synonym
15th century, in the meaning defined at sense 1
History and Etymology for synonym
Middle English sinonyme, from Latin synonymum, from Greek synōnymon, from neuter of synōnymos synonymous, from syn- + onyma name — more at NAME
First Known Use of antonym
1857, in the meaning defined above
History and Etymology for antonym
borrowed from French antonyme, probably back-formation from antonymie "opposition of words with contrary senses," borrowed from Greek antōnymía "pronoun (i.e., a word substituting for another), interchange of names," from ant-, anti- "in opposition to, in place of" + -ōnymos "having a name (of the kind specified)" + -ia -IA entry 1 — more at ANTI-, HOMONYMOUS
Some Differences Between Synonyms and Antonyms
The English language (and, we may presume, many other languages) has both antonyms and synonyms. There are many more words with synonyms than there are words with antonyms, since many things exist which do not have an opposite (the word sandwich, for instance, may be said to have synonyms in the words hoagie, grinder, submarine, and many other words, but there is no opposite of sandwich).
Antonym is also a much more recent addition to English than synonym is; it first appeared in the 1860s, whereas synonym has been used for more than 500 years. Additionally, both nouns have adjectival forms: synonymous and antonymous. Synonymous, which is often used loosely ("She has become synonymous with good taste"), is the more common of the two.
First Known Use of homonym
1697, in the meaning defined at sense 1a
History and Etymology for homonym
Latin homonymum, from Greek homōnymon, from neuter of homōnymos
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