synonymist vs lexicologist

synonymist and lexicologist both are nouns.

Word	Noun	Adjective	Verb	Adverb
synonymist	Yes	No	No	No
lexicologist	Yes	No	No	No

As nouns, lexicologist is a hypernym of synonymist; that is, lexicologist is a word with a broader meaning than synonymist:

synonymist: a student of synonyms
lexicologist: a compiler or writer of a dictionary; a student of the lexical component of language

Other hypernyms of synonymist include lexicographer.

synonymist (noun)	lexicologist (noun)
a student of synonyms	a compiler or writer of a dictionary; a student of the lexical component of language