Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
defencelessly is an adverb meaning "without defense". It carries one recorded sense.
without defense
“the child was standing in the middle of the crossfire, defenselessly”
Definitions, synonyms and semantic relations for defencelessly come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.