Source : Webster's Revised Unabridged Dictionary (1913)

Spanking \Spank"ing\, a.
   1. Moving with a quick, lively pace, or capable of so doing;
      dashing.

            Four spanking grays ready harnessed.  --G. Colman,
                                                  the Younger.

   2. Large; considerable. [Colloq.]

Spank \Spank\, v. t. [imp. & p. p. {Spanked}; 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.

Source : WordNet®

spanking
     adj : 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: {brisk}, {lively},
            {merry}, {rattling}, {snappy}, {zippy}]
     n : the act of slapping on the buttocks; "he gave the brat a
         good spanking"