'Sea pen' definitions:

Definition of 'sea pen'

noun

Fleshy featherlike warm-water colonies

From: GCIDE

Pen \Pen\ (p[e^]n), n. [OE. penne, OF. penne, pene, F. penne, fr. L. penna.]
1. A feather. [Obs.] --Spenser. [1913 Webster]
2. A wing. [Obs.] --Milton. [1913 Webster]
3. 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. [1913 Webster]
Graven with an iron pen and lead in the rock. --Job xix. 24. [1913 Webster]
4. Fig.: A writer, or his style; as, he has a sharp pen. "Those learned pens." --Fuller. [1913 Webster]
5. (Zool.) The internal shell of a squid. [1913 Webster]
6. [Etymol. uncertain.] (Zool.) A female swan; -- contrasted with cob, the male swan. [Prov. Eng.] [1913 Webster]
Bow pen. See Bow-pen.
Dotting pen, a pen for drawing dotted lines.
Drawing pen, 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 (Zool.), a pennatula. [Usually written sea-pen.] [1913 Webster]