The Collaborative International Dictionary of English v.0.48:

Horn \Horn\ (h[^o]rn), n. [AS. horn; akin to D. horen, hoorn,
   G., Icel., Sw., & Dan. horn, Goth. ha['u]rn, W., Gael., & Ir.
   corn, L. cornu, Gr. ke`ras, and perh. also to E. cheer,
   cranium, cerebral; cf. Skr. [,c]iras head. Cf. Carat,
   Corn on the foot, Cornea, Corner, Cornet,
   Cornucopia, Hart.]
   1. A hard, projecting, and usually pointed organ, growing
      upon the heads of certain animals, esp. of the ruminants,
      as cattle, goats, and the like. The hollow horns of the Ox
      family consist externally of true horn, and are never
      shed.
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   2. The antler of a deer, which is of bone throughout, and
      annually shed and renewed.
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   3. (Zool.) Any natural projection or excrescence from an
      animal, resembling or thought to resemble a horn in
      substance or form; esp.:
      (a) A projection from the beak of a bird, as in the
          hornbill.
      (b) A tuft of feathers on the head of a bird, as in the
          horned owl.
      (c) A hornlike projection from the head or thorax of an
          insect, or the head of a reptile, or fish.
      (d) A sharp spine in front of the fins of a fish, as in
          the horned pout.
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   4. (Bot.) An incurved, tapering and pointed appendage found
      in the flowers of the milkweed (Asclepias).
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   5. Something made of a horn, or in resemblance of a horn; as:
      (a) A wind instrument of music; originally, one made of a
          horn (of an ox or a ram); now applied to various
          elaborately wrought instruments of brass or other
          metal, resembling a horn in shape. "Wind his horn
          under the castle wall." --Spenser. See French horn,
          under French.
      (b) A drinking cup, or beaker, as having been originally
          made of the horns of cattle. "Horns of mead and ale."
          --Mason.
      (c) The cornucopia, or horn of plenty. See Cornucopia.
          "Fruits and flowers from Amalth[ae]a's horn."
          --Milton.
      (d) A vessel made of a horn; esp., one designed for
          containing powder; anciently, a small vessel for
          carrying liquids. "Samuel took the hornof oil and
          anointed him [David]." --1 Sam. xvi. 13.
      (e) The pointed beak of an anvil.
      (f) The high pommel of a saddle; also, either of the
          projections on a lady's saddle for supporting the leg.
      (g) (Arch.) The Ionic volute.
      (h) (Naut.) The outer end of a crosstree; also, one of the
          projections forming the jaws of a gaff, boom, etc.
      (i) (Carp.) A curved projection on the fore part of a
          plane.
      (j) One of the projections at the four corners of the
          Jewish altar of burnt offering. "Joab . . . caught
          hold on the horns of the altar." --1 Kings ii. 28.
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   6. One of the curved ends of a crescent; esp., an extremity
      or cusp of the moon when crescent-shaped.
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            The moon
            Wears a wan circle round her blunted horns.
                                                  --Thomson.
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   7. (Mil.) The curving extremity of the wing of an army or of
      a squadron drawn up in a crescentlike form.
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            Sharpening in mooned horns
            Their phalanx.                        --Milton.
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   8. The tough, fibrous material of which true horns are
      composed, being, in the Ox family, chiefly albuminous,
      with some phosphate of lime; also, any similar substance,
      as that which forms the hoof crust of horses, sheep, and
      cattle; as, a spoon of horn.
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   9. (Script.) A symbol of strength, power, glory, exaltation,
      or pride.
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            The Lord is . . . the horn of my salvation. --Ps.
                                                  xviii. 2.
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   10. An emblem of a cuckold; -- used chiefly in the plural.
       "Thicker than a cuckold's horn." --Shak.
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   11. the telephone; as, on the horn. [slang]
       [PJC]

   12. a body of water shaped like a horn; as, the Golden Horn
       in Istanbul.
       [PJC]

   Horn block, the frame or pedestal in which a railway car
      axle box slides up and down; -- also called horn plate.


   Horn of a dilemma. See under Dilemma.

   Horn distemper, a disease of cattle, affecting the internal
      substance of the horn.

   Horn drum, a wheel with long curved scoops, for raising
      water.

   Horn lead (Chem.), chloride of lead.

   Horn maker, a maker of cuckolds. [Obs.] --Shak.

   Horn mercury. (Min.) Same as Horn quicksilver (below).

   Horn poppy (Bot.), a plant allied to the poppy (Glaucium
      luteum), found on the sandy shores of Great Britain and
      Virginia; -- called also horned poppy. --Gray.

   Horn pox (Med.), abortive smallpox with an eruption like
      that of chicken pox.

   Horn quicksilver (Min.), native calomel, or bichloride of
      mercury.

   Horn shell (Zool.), any long, sharp, spiral, gastropod
      shell, of the genus Cerithium, and allied genera.

   Horn silver (Min.), cerargyrite.

   Horn slate, a gray, siliceous stone.

   To pull in one's horns, To haul in one's horns, to
      withdraw some arrogant pretension; to cease a demand or
      withdraw an assertion. [Colloq.]

   To raise the horn, or To lift the horn (Script.), to
      exalt one's self; to act arrogantly. "'Gainst them that
      raised thee dost thou lift thy horn?" --Milton.

   To take a horn, to take a drink of intoxicating liquor.
      [Low]
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