The Collaborative International Dictionary of English v.0.48:

Flask \Flask\ (fl[a^]sk or fl[.a]sk), n. [AS. flasce, flaxe;
   akin to D. flesch, OHG. flasca, G. flasche, Icel. & Sw.
   flaska, Dan. flaske, OF. flasche, LL. flasca, flasco; of
   uncertain origin; cf. L. vasculum, dim. of vas a vessel, Gr.
   fla`skh, fla`skwn, fla`skion. Cf. Flagon, Flasket.]
   1. A small bottle-shaped vessel for holding fluids; as, a
      flask of oil or wine.
      [1913 Webster]

   2. A narrow-necked vessel of metal or glass, used for various
      purposes; as of sheet metal, to carry gunpowder in; or of
      wrought iron, to contain quicksilver; or of glass, to heat
      water in, etc.
      [1913 Webster]

   3. A bed in a gun carriage. [Obs.] --Bailey.
      [1913 Webster]

   4. (Founding) The wooden or iron frame which holds the sand,
      etc., forming the mold used in a foundry; it consists of
      two or more parts; viz., the cope or top; sometimes, the
      cheeks, or middle part; and the drag, or bottom part. When
      there are one or more cheeks, the flask is called a three
      part flask, four part flask, etc.
      [1913 Webster]

   Erlenmeyer flask, a thin glass flask, flat-bottomed and
      cone-shaped to allow of safely shaking its contents
      laterally without danger of spilling; -- so called from
      Erlenmeyer, a German chemist who invented it.

   Florence flask. [From Florence in Italy.]
      (a) Same as Betty, n., 3.
      (b) A glass flask, round or pear-shaped, with round or
          flat bottom, and usually very thin to allow of heating
          solutions.

   Pocket flask, a kind of pocket dram bottle, often covered
      with metal or leather to protect it from breaking.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pocket flask
    n 1: a flask that holds spirits [syn: hipflask, pocket
         flask]