toponomy vs toponymy

toponomy and toponymy both are nouns.

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

As nouns, toponomy and toponymy are synonyms defined as:

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

As nouns, toponomy and toponymy are synonyms defined as:

toponomy (noun)	toponymy (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