Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
hereupon is an adverb meaning "immediately after this". It carries one recorded sense.
immediately after this
“hereupon, the passengers stumbled aboard”
Definitions, synonyms and semantic relations for hereupon come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.