The Collaborative International Dictionary of English v.0.48:

Cool \Cool\, a. [Compar. Cooler; superl. Coolest.] [AS.
   c[=o]l; akin to D. koel, G. k["u]hl, OHG. chouli, Dan.
   k["o]lig, Sw. kylig, also to AS. calan to be cold, Icel.
   kala. See Cold, and cf. Chill.]
   1. Moderately cold; between warm and cold; lacking in warmth;
      producing or promoting coolness.
      [1913 Webster]

            Fanned with cool winds.               --Milton.
      [1913 Webster]

   2. Not ardent, warm, fond, or passionate; not hasty;
      deliberate; exercising self-control; self-possessed;
      dispassionate; indifferent; as, a cool lover; a cool
      debater.
      [1913 Webster]

            For a patriot, too cool.              --Goldsmith.
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   3. Not retaining heat; light; as, a cool dress.
      [1913 Webster]

   4. Manifesting coldness or dislike; chilling; apathetic; as,
      a cool manner.
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   5. Quietly impudent; negligent of propriety in matters of
      minor importance, either ignorantly or willfully;
      presuming and selfish; audacious; as, cool behavior.
      [1913 Webster]

            Its cool stare of familiarity was intolerable.
                                                  --Hawthorne.
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   6. Applied facetiously, in a vague sense, to a sum of money,
      commonly as if to give emphasis to the largeness of the
      amount.
      [1913 Webster]

            He had lost a cool hundred.           --Fielding.
      [1913 Webster]

            Leaving a cool thousand to Mr. Matthew Pocket.
                                                  --Dickens.

   Syn: Calm; dispassionate; self-possessed; composed;
        repulsive; frigid; alienated; impudent.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cooler \Cool"er\, n.
   That which cools, or abates heat or excitement.
   [1913 Webster]

         If acid things were used only as coolers, they would
         not be so proper in this case.           --Arbuthnot.
   [1913 Webster]

   2. Anything in or by which liquids or other things are
      cooled, as an ice chest, a vessel for ice water, etc.
      [1913 Webster]

   3. An alcoholic beverage containing liquor or wine plus a
      carbonated beverage, usually served with ice.
      [PJC]

   4. jail; -- usually used in the form the cooler. [slang]
      [PJC]

   4. an air conditioner.
      [PJC] cool-headed

WordNet (r) 3.0 (2006):

cooler
    n 1: a refrigerator for cooling liquids [syn: cooler, ice
         chest]
    2: an iced drink especially white wine and fruit juice
    3: a cell for violent prisoners [syn: cooler, tank]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "cooler":
   air cooler, calaboose, can, chiller, chokey, clink, cold pack,
   coop, fan, hoosegow, ice bag, ice bucket, ice cube, ice pack,
   ice pail, jug, lockup, pokey, prison, quod, slammer, stir,
   surface cooler, ventilator, water cooler, wine cooler