Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
acheronian is an adjective meaning "dark and dismal as of the rivers Acheron and Styx in Hades". It carries one recorded sense.
dark and dismal as of the rivers Acheron and Styx in Hades
“in the depths of an Acheronian forest”
“upon those roseate lips a Stygian hue”
Definitions, synonyms and semantic relations for acheronian come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.