synonymy vs synonymity

synonymy and synonymity both are nouns.

Word	Noun	Adjective	Verb	Adverb
synonymy	Yes	No	No	No
synonymity	Yes	No	No	No

As nouns, synonymy and synonymity are synonyms defined as:

synonymy and synonymity: the semantic relation that holds between two words that can (in a given context) express the same meaning

Other synonyms of synonymy include synonymousness.

synonymy (noun)	synonymity (noun)
the semantic relation that holds between two words that can (in a given context) express the same meaning	the semantic relation that holds between two words that can (in a given context) express the same meaning