synonymousness vs synonymity

synonymousness and synonymity both are nouns.

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

As nouns, synonymousness and synonymity are synonyms defined as:

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

Other synonyms of synonymousness include synonymy.

synonymousness (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