Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
foster-sister is a noun meaning "your foster sister is a female who is not a daughter of your parents but who is raised by your parents". It carries one recorded sense.
your foster sister is a female who is not a daughter of your parents but who is raised by your parents
Definitions, synonyms and semantic relations for foster-sister come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.