Source : Webster's Revised Unabridged Dictionary (1913)

Keen \Keen\ (k[=e]n), a. [Compar. {Keener} (-[~e]r); superl.
   {Keenest}.] [OE. kene sharp, bold, AS. c[=e]ne bold; akin to
   D. koen, OHG. kuoni, G. k["u]hn, OSw. kyn, k["o]n, Icel.
   k[ae]nn, for k[oe]nn wise; perh. akin to E. ken, can to be
   able. [root]45. ]
   1. Sharp; having a fine edge or point; as, a keen razor, or a
      razor with a keen edge.

            A bow he bare and arwes [arrows] bright and kene.
                                                  --Chaucer.

            That my keen knife see not the wound it makes.
                                                  --Shak.

   2. Acute of mind; sharp; penetrating; having or expressing
      mental acuteness; as, a man of keen understanding; a keen
      look; keen features.

            To make our wits more keen.           --Shak.

            Before the keen inquiry of her thought. --Cowper.

   3. Bitter; piercing; acrimonious; cutting; stinging; severe;
      as, keen satire or sarcasm.

            Good father cardinal, cry thou amen To my keen
            curses.                               --Shak.

   4. Piercing; penetrating; cutting; sharp; -- applied to cold,
      wind, etc,; as, a keen wind; the cold is very keen.

            Breasts the keen air, and carols as he goes.
                                                  --Goldsmith.

   5. Eager; vehement; fierce; as, a keen appetite. ``Of full
      kene will.'' --Piers Plowman.

            So keen and greedy to confound a man. --Shak.

   Note: Keen is often used in the composition of words, most of
         which are of obvious signification; as, keen-edged,
         keen-eyed, keen-sighted, keen-witted, etc.

   Syn: Prompt; eager; ardent; sharp; acute; cutting;
        penetrating; biting; severe; sarcastic; satirical;
        piercing; shrewd.

Keener \Keen"er\, n.
   A professional mourner who wails at a funeral. [Ireland]