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.

Keen \Keen\, v. t.
   To sharpen; to make cold. [R.]

         Cold winter keens the brightening flood. --Thomson.

Keen \Keen\, n. [Ir. caoine.]
   A prolonged wail for a deceased person. Cf. {Coranach}.
   [Ireland] --Froude.

Keen \Keen\, v. i.
   To wail as a keener does. [Ireland]

Source : WordNet®

keen
     v : express grief verbally; "we lamented the death of the child"
         [syn: {lament}]

keen
     n : a funeral lament sung with loud wailing

keen
     adj 1: having or demonstrating ability to recognize or draw fine
            distinctions; "an acute observer of politics and
            politicians"; "incisive comments"; "icy knifelike
            reasoning"; "as sharp and incisive as the stroke of a
            fang"; "penetrating insight"; "frequent penetrative
            observations" [syn: {acute}, {discriminating}, {incisive},
             {knifelike}, {penetrating}, {penetrative}, {piercing},
             {sharp}]
     2: intense or sharp; "suffered exquisite pain"; "felt exquisite
        pleasure" [syn: {exquisite}]
     3: very penetrating and clear and sharp in operation; "an
        incisive mind"; "a keen intelligence"; "of sharp and
        active intellect" [syn: {incisive}, {sharp}]
     4: very good; "he did a bully job"; "a neat sports car"; "had a
        great time at the party"; "you look simply smashing" [syn:
         {bang-up}, {bully}, {corking}, {cracking}, {dandy}, {great},
         {groovy}, {neat}, {nifty}, {not bad(p)}, {peachy}, {slap-up},
         {swell}, {smashing}]
     5: as physically painful as if caused by a sharp instrument; "a
        cutting wind"; "keen winds"; "knifelike cold"; "piercing
        knifelike pains"; "piercing cold"; "piercing criticism";
        "a stabbing pain"; "lancinating pain" [syn: {cutting}, {knifelike},
         {piercing}, {stabbing}, {lancinate}, {lancinating}]
     6: having a sharp cutting edge or point; "a keen blade"