Plagiarize, 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).
Shades of meaning
Fernald has no entry of its own for plagiarize; he lists it under quote.
Where he writes about it:
One may paraphrase a work with worthy motive for homiletic, devotional, or other purposes (as in the metrical versions of the Psalms), or he may plagiarize atrociously in the form of paraphrase, appropriating all that is valuable in another's thought, with the hope of escaping detection by change of phrase. — from quote
To plagiarize is to quote without credit, appropriating another's words or thought as one's own. — from quote