toponymy vs lexicology

toponymy and lexicology both are nouns.

Word	Noun	Adjective	Verb	Adverb
toponymy	Yes	No	No	No
lexicology	Yes	No	No	No

As nouns, lexicology is a hypernym of toponymy; that is, lexicology is a word with a broader meaning than toponymy:

toponymy: the branch of lexicology that studies the place names of a region or a language
lexicology: the branch of linguistics that studies the lexical component of language

toponymy (noun)	lexicology (noun)
the branch of lexicology that studies the place names of a region or a language	the branch of linguistics that studies the lexical component of language
the nomenclature of regional anatomy