instantaneousness vs immediacy

instantaneousness and immediacy both are nouns.

Word	Noun	Adjective	Verb	Adverb
instantaneousness	Yes	No	No	No
immediacy	Yes	No	No	No

As nouns, instantaneousness and immediacy are synonyms defined as:

Other synonyms of instantaneousness include immediateness, instancy.

instantaneousness (noun)	immediacy (noun)
the quickness of action or occurrence	the quickness of action or occurrence
	lack of an intervening or mediating agency
	immediate intuitive awareness