Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
senselessly is an adverb meaning "in a meaningless and purposeless manner". It carries 2 recorded senses.
in a meaningless and purposeless manner
“these innocent bystanders were senselessly killed”
in an unreasonably senseless manner
“these temples were mindlessly destroyed by the Red Guards”
Definitions, synonyms and semantic relations for senselessly come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.