Source : Webster's Revised Unabridged Dictionary (1913)

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.

            Fanned with cool winds.               --Milton.

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

            For a patriot, too cool.              --Goldsmith.

   3. Not retaining heat; light; as, a cool dress.

   4. Manifesting coldness or dislike; chilling; apathetic; as,
      a cool manner.

   5. Quietly impudent; negligent of propriety in matters of
      minor importance, either ignorantly or willfully;
      presuming and selfish; audacious; as, cool behavior.

            Its cool stare of familiarity was intolerable.
                                                  --Hawthorne.

   6. Applied facetiously, in a vague sense, to a sum of money,
      commonly as if to give emphasis to the largeness of the
      amount.

            He had lost a cool hundred.           --Fielding.

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

   Syn: Calm; dispassionate; self-possessed; composed;
        repulsive; frigid; alienated; impudent.