The Collaborative International Dictionary of English v.0.48:

Drop \Drop\ (dr[o^]p), n. [OE. drope, AS. dropa; akin to OS.
   dropo, D. drop, OHG. tropo, G. tropfen, Icel. dropi, Sw.
   droppe; and Fr. AS. dre['o]pan to drip, drop; akin to OS.
   driopan, D. druipen, OHG. triofan, G. triefen, Icel.
   drj[=u]pa. Cf. Drip, Droop.]
   1. The quantity of fluid which falls in one small spherical
      mass; a liquid globule; a minim; hence, also, the smallest
      easily measured portion of a fluid; a small quantity; as,
      a drop of water.
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            With minute drops from off the eaves. --Milton.
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            As dear to me as are the ruddy drops
            That visit my sad heart.              -- Shak.
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            That drop of peace divine.            --Keble.
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   2. That which resembles, or that which hangs like, a liquid
      drop; as a hanging diamond ornament, an earring, a glass
      pendant on a chandelier, a sugarplum (sometimes
      medicated), or a kind of shot or slug.
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   3. (Arch.)
      (a) Same as Gutta.
      (b) Any small pendent ornament.
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   4. Whatever is arranged to drop, hang, or fall from an
      elevated position; also, a contrivance for lowering
      something; as:
      (a) A door or platform opening downward; a trap door; that
          part of the gallows on which a culprit stands when he
          is to be hanged; hence, the gallows itself.
      (b) A machine for lowering heavy weights, as packages,
          coal wagons, etc., to a ship's deck.
      (c) A contrivance for temporarily lowering a gas jet.
      (d) A curtain which drops or falls in front of the stage
          of a theater, etc.
      (e) A drop press or drop hammer.
      (f) (Mach.) The distance of the axis of a shaft below the
          base of a hanger.
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   5. pl. Any medicine the dose of which is measured by drops;
      as, lavender drops.
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   6. (Naut.) The depth of a square sail; -- generally applied
      to the courses only. --Ham. Nav. Encyc.
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   7. Act of dropping; sudden fall or descent.
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   Ague drop, Black drop. See under Ague, Black.

   Drop by drop, in small successive quantities; in repeated
      portions. "Made to taste drop by drop more than the
      bitterness of death." --Burke.

   Drop curtain. See Drop, n., 4.
      (d) .

   Drop forging. (Mech.)
      (a) A forging made in dies by a drop hammer.
      (b) The process of making drop forgings.

   Drop hammer (Mech.), a hammer for forging, striking up
      metal, etc., the weight being raised by a strap or similar
      device, and then released to drop on the metal resting on
      an anvil or die.

   Drop kick (Football), a kick given to the ball as it
      rebounds after having been dropped from the hands.

   Drop lake, a pigment obtained from Brazil wood. --Mollett.

   Drop letter, a letter to be delivered from the same office
      where posted.

   Drop press (Mech.), a drop hammer; sometimes, a dead-stroke
      hammer; -- also called drop.

   Drop scene, a drop curtain on which a scene is painted. See
      Drop, n., 4.
      (d) .

   Drop seed. (Bot.) See the List under Glass.

   Drop serene. (Med.) See Amaurosis.
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WordNet (r) 3.0 (2006):

drop curtain
    n 1: a curtain that can be lowered and raised onto a stage from
         the flies; often used as background scenery [syn: drop
         curtain, drop cloth, drop]