The Collaborative International Dictionary of English v.0.48:

Agile \Ag"ile\, a. [F. agile, L. agilis, fr. agere to move. See
   Agent.]
   Having the faculty of quick motion in the limbs; apt or ready
   to move; nimble; active; as, an agile boy; an agile tongue.
   [1913 Webster]

         Shaking it with agile hand.              --Cowper.
   [1913 Webster]

   Syn: Active; alert; nimble; brisk; lively; quick.
        [1913 Webster]

WordNet (r) 3.0 (2006):

agile
    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:

81 Moby Thesaurus words for "agile":
   active, acute, adroit, alacritous, alert, alive, attentive, awake,
   breakneck, bright, brisk, catty, dashing, deft, dexterous,
   dextrous, dispatchful, double-quick, eagle-winged, expeditious,
   express, fast, featly, fleet, flying, galloping, graceful,
   hair-trigger, hasty, headlong, hustling, keen, light,
   light of heel, light-footed, limber, lissome, lithe, lively,
   mercurial, neat-fingered, neat-handed, nimble, nimble-footed,
   on the, on the alert, on the ball, on the job, peart, precipitate,
   prompt, qui vive, quick, quick as lightning, quick as thought,
   rapid, ready, reckless, resourceful, running, sharp, sleepless,
   smart, snappy, spanking, speedy, sprightly, spry, supple,
   sure-footed, swift, tripping, unblinking, unnodding, unsleeping,
   unwinking, volant, wakeful, wide-awake, winged, zippy