Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
uncertainness is a noun meaning "being unsettled or in doubt or dependent on chance". It carries one recorded sense.
being unsettled or in doubt or dependent on chance
“the uncertainty of the outcome”
“the precariousness of his income”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for uncertainness come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.