Source : Webster's Revised Unabridged Dictionary (1913)

Beagle \Bea"gle\, n. [OE. begele; perh. of Celtic origin; cf.
   Ir. & Gael. beag small, little, W. bach. F. bigle is from
   English.]
   1. A small hound, or hunting dog, twelve to fifteen inches
      high, used in hunting hares and other small game. See
      Illustration in Appendix.

   2. Fig.: A spy or detective; a constable.

Source : WordNet®

beagle
     n : a small short-legged smooth-coated breed of hound