synonymity vs semantic relation

synonymity and semantic relation both are nouns.

Word	Noun	Adjective	Verb	Adverb
synonymity	Yes	No	No	No
semantic relation	Yes	No	No	No

As nouns, semantic relation is a hypernym of synonymity; that is, semantic relation is a word with a broader meaning than synonymity:

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

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