Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
presumptuousness is a noun meaning "audacious (even arrogant) behavior that you have no right to". It carries one recorded sense.
audacious (even arrogant) behavior that you have no right to
“he despised them for their presumptuousness”
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 presumptuousness come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.