Source : Webster's Revised Unabridged Dictionary (1913)

   {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} (Zo["o]l.), a pennatula. [Usually written
      {sea-pen}.]

Source : WordNet®

sea pen
     n : fleshy featherlike warm-water colonies