The Collaborative International Dictionary of English v.0.48:

Pen \Pen\, v. t. [imp. & p. p. Penned; p. pr. & vb. n.
   Penning.]
   To write; to compose and commit to paper; to indite; to
   compose; as, to pen a sonnet. "A prayer elaborately penned."
   --Milton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pen \Pen\, v. t. [imp. & p. p. Pennedor Pent (?); p. pr. &
   vb. n. Penning.] [OE. pennen, AS. pennan in on-pennan to
   unfasten, prob. from the same source as pin, and orig.
   meaning, to fasten with a peg.See Pin, n. & v.]
   To shut up, as in a pen or cage; to confine in a small
   inclosure or narrow space; to coop up, or shut in; to
   inclose. "Away with her, and pen her up." --Shak.
   [1913 Webster]

         Watching where shepherds pen their flocks at eve.
                                                  --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

penning
    n 1: the act of creating written works; "writing was a form of
         therapy for him"; "it was a matter of disputed authorship"
         [syn: writing, authorship, composition, penning]