synonymousness vs synonymy

synonymousness and synonymy both are nouns.

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

As nouns, synonymousness and synonymy are synonyms defined as:

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

Other synonyms of synonymousness include synonymity.

synonymousness (noun)	synonymy (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