Wiktionary
half sister
n. 1 The daughter of one's mother who has a different father, maternal half sister, uterine sister 2 The daughter of one's father who has a different mother, paternal half sister.
WordNet
half sister
n. a sister who has only one parent in common with you [syn: stepsister]
Usage examples of "half sister".
She was blood kin of the Antes house, favored second cousin of Ivanova, half sister to Prince Rodek.