Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
powerfulness is a noun meaning "possession of controlling influence". It carries one recorded sense.
possession of controlling influence
“the deterrent power of nuclear weapons”
“the power of his love saved her”
“his powerfulness was concealed by a gentle facade”
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 powerfulness come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.