Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
unassertively is an adverb meaning "in an unassertive manner". It carries one recorded sense.
in an unassertive manner
“unassertively, she always follows her husband's suggestions”
Definitions, synonyms and semantic relations for unassertively come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.