Source : Webster's Revised Unabridged Dictionary (1913)

Ounce \Ounce\, n. [F. once, fr. L. uncia a twelfth, the twelfth
   part of a pound or of a foot: cf. Gr. ? bulk, mass, atom. Cf.
   2d {Inch}, {Oke}.]
   1. A weight, the sixteenth part of a pound avoirdupois, and
      containing 437? grains.

   2. (Troy Weight) The twelfth part of a troy pound.

   Note: The troy ounce contains twenty pennyweights, each of
         twenty-four grains, or, in all, 480 grains, and is the
         twelfth part of the troy pound. The troy ounce is also
         a weight in apothecaries' weight. [Troy ounce is
         sometimes written as one word, {troyounce}.]

   3. Fig.: A small portion; a bit. [Obs.]

            By ounces hung his locks that he had. --Chaucer.

   {Fluid ounce}. See under {Fluid}, n.

Fluid \Flu"id\, n.
   A fluid substance; a body whose particles move easily among
   themselves.

   Note: Fluid is a generic term, including liquids and gases as
         species. Water, air, and steam are fluids. By analogy,
         the term is sometimes applied to electricity and
         magnetism, as in phrases electric fluid, magnetic
         fluid, though not strictly appropriate.

   {Fluid dram}, or {Fluid drachm}, a measure of capacity equal
      to one eighth of a fluid ounce.

   {Fluid ounce}.
   (a) In the United States, a measure of capacity, in
       apothecaries' or wine measure, equal to one sixteenth of
       a pint or 29.57 cubic centimeters. This, for water, is
       about 1.04158 ounces avoirdupois, or 455.6 grains.
   (b) In England, a measure of capacity equal to the twentieth
       part of an imperial pint. For water, this is the weight
       of the avoirdupois ounce, or 437.5 grains.

   {Fluids of the body}. (Physiol.) The circulating blood and
      lymph, the chyle, the gastric, pancreatic, and intestinal
      juices, the saliva, bile, urine, aqueous humor, and muscle
      serum are the more important fluids of the body. The
      tissues themselves contain a large amount of combined
      water, so much, that an entire human body dried in vacuo
      with a very moderate degree of heat gives about 66 per
      cent of water.

   {Burning fluid}, {Elastic fluid}, {Electric fluid}, {Magnetic
   fluid}, etc. See under {Burning}, {Elastic}, etc.

Source : WordNet®

fluid ounce
     n 1: a British imperial unit of capacity or volume (liquid or
          dry) equal to 8 fluid drams or 28.416 cubic centimeters
          (1.734 cubic inches) [syn: {fluidounce}]
     2: a United States unit of capacity or volume equal to 1.804
        cubic inches [syn: {fluidounce}]