simultaneousness vs simultaneity

simultaneousness and simultaneity both are nouns.

Word	Noun	Adjective	Verb	Adverb
simultaneousness	Yes	No	No	No
simultaneity	Yes	No	No	No

As nouns, simultaneousness and simultaneity are synonyms defined as:

simultaneousness and simultaneity: happening or existing or done at the same time

simultaneousness (noun)	simultaneity (noun)
happening or existing or done at the same time	happening or existing or done at the same time