Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
rightfulness is a noun meaning "anything in accord with principles of justice". It carries one recorded sense.
anything in accord with principles of justice
“he feels he is in the right”
“the rightfulness of his claim”
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 rightfulness come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.