The Collaborative International Dictionary of English v.0.48:

Sheet anchor \Sheet" an"chor\ [OE. scheten to shoot, AS.
   sce['o]tan; cf. OE. shoot anchor. See Shoot, v. t.]
   1. (Naut.) A large anchor stowed on shores outside the waist
      of a vessel; -- called also waist anchor. See the Note
      under Anchor.
      [1913 Webster]

   2. Anything regarded as a sure support or dependence in
      danger; the best hope or refuge.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Waist \Waist\, n. [OE. wast; originally, growth, akin to AS.
   weaxan to grow; cf. AS. w[ae]stm growth. See Wax to grow.]
   [1913 Webster]
   1. That part of the human body which is immediately below the
      ribs or thorax; the small part of the body between the
      thorax and hips. --Chaucer.
      [1913 Webster]

            I am in the waist two yards about.    --Shak.
      [1913 Webster]

   2. Hence, the middle part of other bodies; especially
      (Naut.), that part of a vessel's deck, bulwarks, etc.,
      which is between the quarter-deck and the forecastle; the
      middle part of the ship.
      [1913 Webster]

   3. A garment, or part of a garment, which covers the body
      from the neck or shoulders to the waist line.
      [1913 Webster]

   4. A girdle or belt for the waist. [Obs.] --Shak.
      [1913 Webster]

   Waist anchor. See Sheet anchor, 1, in the Vocabulary.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Anchor \An"chor\ ([a^][ng]"k[~e]r), n. [OE. anker, AS. ancor,
   oncer, L. ancora, sometimes spelt anchora, fr. Gr. 'a`gkyra,
   akin to E. angle: cf. F. ancre. See Angle, n.]
   1. A iron instrument which is attached to a ship by a cable
      (rope or chain), and which, being cast overboard, lays
      hold of the earth by a fluke or hook and thus retains the
      ship in a particular station.
      [1913 Webster]

   Note: The common anchor consists of a straight bar called a
         shank, having at one end a transverse bar called a
         stock, above which is a ring for the cable, and at the
         other end the crown, from which branch out two or more
         arms with flukes, forming with the shank a suitable
         angle to enter the ground.
         [1913 Webster]

   Note: Formerly the largest and strongest anchor was the sheet
         anchor (hence, Fig., best hope or last refuge), called
         also waist anchor. Now the bower and the sheet anchor
         are usually alike. Then came the best bower and the
         small bower (so called from being carried on the bows).
         The stream anchor is one fourth the weight of the bower
         anchor. Kedges or kedge anchors are light anchors used
         in warping.
         [1913 Webster]

   2. Any instrument or contrivance serving a purpose like that
      of a ship's anchor, as an arrangement of timber to hold a
      dam fast; a contrivance to hold the end of a bridge cable,
      or other similar part; a contrivance used by founders to
      hold the core of a mold in place.
      [1913 Webster]

   3. Fig.: That which gives stability or security; that on
      which we place dependence for safety.
      [1913 Webster]

            Which hope we have as an anchor of the soul. --Heb.
                                                  vi. 19.
      [1913 Webster]

   4. (Her.) An emblem of hope.
      [1913 Webster]

   5. (Arch.)
      (a) A metal tie holding adjoining parts of a building
          together.
      (b) Carved work, somewhat resembling an anchor or
          arrowhead; -- a part of the ornaments of certain
          moldings. It is seen in the echinus, or egg-and-anchor
          (called also egg-and-dart, egg-and-tongue)
          ornament.
          [1913 Webster]

   6. (Zool.) One of the anchor-shaped spicules of certain
      sponges; also, one of the calcareous spinules of certain
      Holothurians, as in species of Synapta.
      [1913 Webster]

   6. (Television) an achorman, anchorwoman, or
      anchorperson.
      [1913 Webster]

   Anchor ice. See under Ice.

   Anchor light See the vocabulary.

   Anchor ring. (Math.) Same as Annulus, 2 (b).

   Anchor shot See the vocabulary.

   Anchor space See the vocabulary.

   Anchor stock (Naut.), the crossbar at the top of the shank
      at right angles to the arms.

   Anchor watch See the vocabulary.

   The anchor comes home, when it drags over the bottom as the
      ship drifts.

   Foul anchor, the anchor when it hooks, or is entangled
      with, another anchor, or with a cable or wreck, or when
      the slack cable is entangled.

   The anchor is acockbill, when it is suspended
      perpendicularly from the cathead, ready to be let go.

   The anchor is apeak, when the cable is drawn in so tight as
      to bring the ship directly over it.

   The anchor is atrip, or aweigh, when it is lifted out of
      the ground.

   The anchor is awash, when it is hove up to the surface of
      the water.

   At anchor, anchored.

   To back an anchor, to increase the holding power by laying
      down a small anchor ahead of that by which the ship rides,
      with the cable fastened to the crown of the latter to
      prevent its coming home.

   To cast anchor, to drop or let go an anchor to keep a ship
      at rest.

   To cat the anchor, to hoist the anchor to the cathead and
      pass the ring-stopper.

   To fish the anchor, to hoist the flukes to their resting
      place (called the bill-boards), and pass the shank
      painter.

   To weigh anchor, to heave or raise the anchor so as to sail
      away.
      [1913 Webster]

WordNet (r) 3.0 (2006):

waist anchor
    n 1: spare anchor for use in emergency [syn: sheet anchor,
         waist anchor]