simultaneity vs simultaneousness

simultaneity and simultaneousness both are nouns.

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

As nouns, simultaneity and simultaneousness are synonyms defined as:

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

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