uncertainty vs uncertainness

uncertainty and uncertainness both are nouns.

Word	Noun	Adjective	Verb	Adverb
uncertainty	Yes	No	No	No
uncertainness	Yes	No	No	No

As nouns, uncertainty and uncertainness are synonyms defined as:

uncertainty and uncertainness: being unsettled or in doubt or dependent on chance

Other synonyms of uncertainty include precariousness.

uncertainty (noun)	uncertainness (noun)
being unsettled or in doubt or dependent on chance	being unsettled or in doubt or dependent on chance
the state of being unsure of something