being vs possibleness

being and possibleness both are nouns.

Word	Noun	Adjective	Verb	Adverb
being	Yes	No	No	No
possibleness	Yes	No	No	No

As nouns, possibleness is a hyponym of being; that is, possibleness is a word with a more specific, narrower meaning than being:

being (noun)	possibleness (noun)
a living thing that has (or can develop) the ability to act or function independently	capability of existing or happening or being true
the state or fact of existing