from
The Collaborative International Dictionary of English v.0.48
Pen \Pen\, v. t. [imp. & p. p. {Penned}or {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]