toponymy vs toponomy

toponymy and toponomy both are nouns.

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

As nouns, toponymy and toponomy are synonyms defined as:

toponymy and toponomy: the branch of lexicology that studies the place names of a region or a language

As nouns, toponymy and toponomy are synonyms defined as:

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