step-sister

/S T EH1 P S IH0 S T ER0/
noun
  1. 1

    The daughter of one's stepparent who is not the daughter of either of one's parents.

  2. 2

    The stepdaughter of one's parent which is not one's half-sister.

Synonyms

Source: https://en.wiktionary.org/wiki/step-sister, https://en.wiktionary.org/wiki/stepsister