The Collaborative International Dictionary of English v.0.48:

spanking \spank"ing\, a.
   1. Moving with a quick, lively pace, or capable of so doing;
      dashing.
      [1913 Webster]

            Four spanking grays ready harnessed.  --G. Colman,
                                                  the Younger.
      [1913 Webster]

   2. Large; considerable. [Colloq.]
      [1913 Webster]

   3. Very; extremely; -- used especially in the phrase spanking
      new or brand spanking new, meaning completely new and
      unused. [informal]
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Spank \Spank\ (sp[a^][ng]k), v. t. [imp. & p. p. Spanked
   (sp[a^][ng]kt); p. pr. & vb. n. Spanking.] [Of unknown
   origin; cf. LG. spakken, spenkern, to run and spring about
   quickly.]
   To strike, as the breech, with the open hand; to slap.
   [1913 Webster]

WordNet (r) 3.0 (2006):

spanking
    adj 1: quick and energetic; "a brisk walk in the park"; "a
           lively gait"; "a merry chase"; "traveling at a rattling
           rate"; "a snappy pace"; "a spanking breeze" [syn:
           alert, brisk, lively, merry, rattling,
           snappy, spanking, zippy]
    n 1: the act of slapping on the buttocks; "he gave the brat a
         good spanking"

Moby Thesaurus II by Grady Ward, 1.0:

180 Moby Thesaurus words for "spanking":
   active, activist, activistic, acute, admonishment, admonition,
   aggressive, agile, alive, animated, awfully, banging, bastinado,
   basting, battery, beating, belting, big, blustery, bouncing,
   bouncy, bracing, brand-new, brand-spanking new, breakneck, breezy,
   bright, brisk, bubbly, buffeting, bumping, caning, castigation,
   chastisement, chiding, chipper, clubbing, corporal punishment,
   correction, cowhiding, crisp, cudgeling, damned, dashing,
   double-quick, dreadfully, drubbing, dynamic, eagle-winged,
   ebullient, effervescent, energetic, enterprising, enthusiastic,
   expeditious, express, extremely, fast, fine, fire-new,
   flagellation, flailing, fleet, flogging, flying, forceful,
   forcible, fresh, freshening, frisky, full of go, full of life,
   full of pep, fustigation, galloping, gleaming, go-go, great,
   hair-trigger, hasty, headlong, hearty, horsewhipping, hustling,
   impetuous, incisive, intense, invigorating, just out, keen,
   kinetic, lacing, large, lashing, lecture, lesson, light of heel,
   light-footed, live, lively, living, lusty, mercurial, mettlesome,
   mightily, militant, newfangle, newfangled, nimble, nimble-footed,
   objurgation, outstanding, peppy, perky, pert, pistol-whipping,
   precipitate, prompt, quick, quick as lightning, quick as thought,
   quicksilver, rapid, rating, rattling, rawhiding, rebuke, reckless,
   remarkable, reprehension, reprimand, reproach, reprobation,
   reproof, reproval, robust, running, scolding, scourging, sermon,
   slapping, smacking, smart, snapping, snappy, spanking new, speedy,
   spirited, sprightly, spry, strapping, strenuous, stripes, strong,
   swift, swingeing, switching, take-charge, take-over, thrashing,
   thumping, thundering, trenchant, trouncing, truncheoning,
   upbraiding, vibrant, vigorous, vivacious, vivid, walloping,
   whacking, whaling, whipping, whopping, winged, zestful, zesty,
   zingy, zippy