The Collaborative International Dictionary of English v.0.48:

Plagiarize \Pla"gia*rize\, v. t. [imp. & p. p. Plagiarized; p.
   pr. & vb. n. Plagiarizing.]
   To steal or purloin from the writings of another; to
   appropriate without due acknowledgement (the ideas or
   expressions of another).
   [1913 Webster]