The Collaborative International Dictionary of English v.0.48:

Sea anchor \Sea" an"chor\ (Naut.)
   See Drag sail, under 4th Drag.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Drag \Drag\, n. [See Drag, v. t., and cf. Dray a cart, and
   1st Dredge.]
   1. The act of dragging; anything which is dragged.
      [1913 Webster]

   2. A net, or an apparatus, to be drawn along the bottom under
      water, as in fishing, searching for drowned persons, etc.
      [1913 Webster]

   3. A kind of sledge for conveying heavy bodies; also, a kind
      of low car or handcart; as, a stone drag.
      [1913 Webster]

   4. A heavy coach with seats on top; also, a heavy carriage.
      [Collog.] --Thackeray.
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   5. A heavy harrow, for breaking up ground.
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   6.
      (a) Anything towed in the water to retard a ship's
          progress, or to keep her head up to the wind; esp., a
          canvas bag with a hooped mouth, so used. See Drag
          sail (below).
      (b) Also, a skid or shoe, for retarding the motion of a
          carriage wheel.
      (c) Hence, anything that retards; a clog; an obstacle to
          progress or enjoyment.
          [1913 Webster]

                My lectures were only a pleasure to me, and no
                drag.                             --J. D.
                                                  Forbes.
          [1913 Webster]

   7. Motion affected with slowness and difficulty, as if
      clogged. "Had a drag in his walk." -- Hazlitt.
      [1913 Webster]

   8. (Founding) The bottom part of a flask or mold, the upper
      part being the cope.
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   9. (Masonry) A steel instrument for completing the dressing
      of soft stone.
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   10. (Marine Engin.) The difference between the speed of a
       screw steamer under sail and that of the screw when the
       ship outruns the screw; or between the propulsive effects
       of the different floats of a paddle wheel. See Citation
       under Drag, v. i., 3.
       [1913 Webster]

   Drag sail (Naut.), a sail or canvas rigged on a stout
      frame, to be dragged by a vessel through the water in
      order to keep her head to the wind or to prevent drifting;
      -- called also drift sail, drag sheet, drag anchor,
      sea anchor, floating anchor, etc.

   Drag twist (Mining), a spiral hook at the end of a rod for
      cleaning drilled holes.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sea anchor
    n 1: restraint consisting of a canvas covered frame that floats
         behind a vessel; prevents drifting or maintains the heading
         into a wind [syn: sea anchor, drogue]