'Stepsister' definitions:

Definition of 'stepsister'

From: WordNet
noun
A sister who has only one parent in common with you [syn: half sister, half-sister, stepsister]

Definition of 'Stepsister'

From: GCIDE
  • Stepsister \Step"sis`ter\, n. A daughter of one's stepfather or stepmother by a former marriage. [1913 Webster]