The Collaborative International Dictionary of English v.0.48:

Keen \Keen\ (k[=e]n), a. [Compar. Keener (k[=e]n"[~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.
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            A bow he bare and arwes [arrows] bright and kene.
                                                  --Chaucer.
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            That my keen knife see not the wound it makes.
                                                  --Shak.
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   2. Acute of mind; sharp; penetrating; having or expressing
      mental acuteness; as, a man of keen understanding; a keen
      look; keen features.
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            To make our wits more keen.           --Shak.
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            Before the keen inquiry of her thought. --Cowper.
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   3. Bitter; piercing; acrimonious; cutting; stinging; severe;
      as, keen satire or sarcasm.
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            Good father cardinal, cry thou amen
            To my keen curses.                    --Shak.
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   4. Piercing; penetrating; cutting; sharp; -- applied to cold,
      wind, etc.; as, a keen wind; the cold is very keen.
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            Breasts the keen air, and carols as he goes.
                                                  --Goldsmith.
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   5. Eager; vehement; fierce; as, a keen appetite. "Of full
      kene will." --Piers Plowman.
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            So keen and greedy to confound a man. --Shak.
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   6. Wonderful; delightful; marvelous; as, that would be keen.
      [slang]
      [PJC]

   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.
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