What does "pen" mean?

Additional senses

1. 2.An instrument used for writing with ink, formerly made of a reed, or of the quill of a goose or other bird, but now also of other materials, as of steel, gold, etc. Also, originally, a stylus or other instrument for scratching or graving. Graven with an iron pen and lead in the rock. Job xix.
2. 3.4. Fig.: A writer, or his style; as, he has a sharp pen. "Those learned pens." Fuller.
3. 4.(Zoöl.) The internal shell of a squid.
4. 5.Etym: [Etymol. uncertain.] (Zoöl.) A female swan. [Prov. Eng.] Bow pen. See Bow-pen. -- Dotting pen, a pen for drawing dotted lines. -- Drawing, or Ruling, pen, a pen for ruling lines having a pair of blades between which the ink is contained. -- Fountain pen, Geometric pen. See under Fountain, and Geometric. -- Music pen, a pen having five points for drawing the five lines of the staff. -- Pen and ink, or pen-and-ink, executed or done with a pen and ink; as, a pen and ink sketch. -- Pen feather. A pin feather. [Obs.] -- Pen name. See under Name. -- Sea pen (Zoöl.), a pennatula. [Usually written sea-pen.]
5. 6.To write; to compose and commit to paper; to indite; to compose; as, to pen a sonnet. "A prayer elaborately penned." Milton.
6. 7.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. Watching where shepherds pen their flocks at eve. Milton.
7. 8.A small inclosure; as, a pen for sheep or for pigs. My father stole two geese out of a pen. Shak.