Source : Webster's Revised Unabridged Dictionary (1913)

Double-quick \Dou"ble-quick`\, a. (Mil.)
   Of, or performed in, the fastest time or step in marching,
   next to the run; as, a double-quick step or march.

Double-quick \Dou"ble-quick`\, n.
   Double-quick time, step, or march.

   Note: Double-quick time requires 165 steps, each 33 inches in
         length, to be taken in one minute. The number of steps
         may be increased up to 180 per minute.

Double-quick \Dou"ble-quick`\, v. i. & t. (Mil.)
   To move, or cause to move, in double-quick time.

Source : WordNet®

double-quick
     adj : (of a marching cadence) very quick