The Collaborative International Dictionary of English v.0.48:

Nimble \Nim"ble\ (n[i^]m"b'l), a. [Compar. Nimbler
   (n[i^]m"bl[~e]r); superl. Nimblest (n[i^]m"bl[e^]st).] [OE.
   nimel, prob. orig., quick at seizing, fr. nimen to take, AS.
   niman; akin to D. nemen, G. nehmen, OHG. neman, Icel. nema,
   Goth. nima, and prob. to Gr. ne`mein to distribute. [root] 7.
   Cf. Nomand, Numb.]
   Light and quick in motion; moving with ease and celerity;
   lively; swift.
   [1913 Webster]

         Through the mid seas the nimble pinnace sails. --Pope.
   [1913 Webster]

   Note: Nimble is sometimes used in the formation of
         self-explaining compounds; as, nimble-footed,
         nimble-pinioned, nimble-winged, etc.
         [1913 Webster]

   Nimble Will (Bot.), a slender, branching, American grass
      (Muhlenbergia diffusa), of some repute for grazing
      purposes in the Mississippi valley.
      [1913 Webster]

   Syn: Agile; quick; active; brisk; lively; prompt.
        [1913 Webster]

WordNet (r) 3.0 (2006):

nimble
    adj 1: moving quickly and lightly; "sleek and agile as a
           gymnast"; "as nimble as a deer"; "nimble fingers"; "quick
           of foot"; "the old dog was so spry it was halfway up the
           stairs before we could stop it" [syn: agile, nimble,
           quick, spry]
    2: mentally quick; "an agile mind"; "nimble wits" [syn: agile,
       nimble]

Moby Thesaurus II by Grady Ward, 1.0:

98 Moby Thesaurus words for "nimble":
   active, acute, adroit, agile, alacritous, alert, alive, apt,
   attentive, awake, brainy, breakneck, bright, brilliant, brisk,
   catty, clever, coruscating, dashing, deft, dexterous, dispatchful,
   double-quick, eagle-winged, energetic, expeditious, express, fast,
   featly, fleet, flying, galloping, gifted, graceful, hair-trigger,
   handy, hasty, headlong, hustling, intelligent, keen, keen-witted,
   light, light of heel, light-footed, lightsome, limber, lithe,
   lively, mercurial, neat-fingered, neat-handed, nimble-footed,
   nimble-witted, no dumbbell, not born yesterday, on the,
   on the alert, on the ball, on the job, peart, precipitate, prompt,
   qui vive, quick, quick as lightning, quick as thought,
   quick-thinking, quick-witted, rapid, ready, reckless, running,
   scintillating, sharp, sharp-witted, sleepless, smart, snappy,
   spanking, sparkling, speedy, sprightly, spry, steel-trap,
   sure-footed, swift, talented, unblinking, unnodding, unsleeping,
   unwinking, vigilant, wakeful, watchful, wide-awake, winged,
   zippy