Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
doubtfulness is a noun meaning "the state of being unsure of something". It carries 2 recorded senses.
the state of being unsure of something
uncertainty about the truth or factuality or existence of something
“the dubiousness of his claim”
“there is no question about the validity of the enterprise”
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 doubtfulness come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.