Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
obsessionally is an adverb meaning "in a compulsive manner". It carries one recorded sense.
in a compulsive manner
“he cleaned his shoes compulsively after every walk”
Definitions, synonyms and semantic relations for obsessionally come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.