The Collaborative International Dictionary of English v.0.48:

Shag \Shag\, v. t. [imp. & p. p. Shagged; p. pr. & vb. n.
   Shagging.]
   To make hairy or shaggy; hence, to make rough.
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         Shag the green zone that bounds the boreal skies. --J.
                                                  Barlow.
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