[1] : The Collaborative International Dictionary of English v.0.48

stepdaughter \step"daugh`ter\, n. as. ste'opdohtor.
   a daughter of one's wife or husband by a former marriage.
   1913 webster

[2] : WordNet (r) 2.0

stepdaughter
     n : a daughter of your spouse by a former marriage

[3] : Bouvier's Law Dictionary, Revised 6th Ed (1856)

step-daughter. in latin privigna, is the daughter of one's wife, or of one's 
husband. 

Stepdaughter >> S Words
Stepdaughter, definition of term: Stepdaughter
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