Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
selflessly is an adverb meaning "in an altruistic manner". It carries one recorded sense.
in an altruistic manner
“he acted selflessly when he helped the old lady in distress”
Definitions, synonyms and semantic relations for selflessly come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.