Source : Webster's Revised Unabridged Dictionary (1913)

Coachwhip snake \Coach"whip` snake"\ (Zo["o]l.)
   A large, slender, harmless snake of the southern United
   States ({Masticophis flagelliformis}).

   Note: Its long and tapering tail has the scales so arranged
         and colored as to give it a braided appearance, whence
         the name.

Source : WordNet®

coachwhip snake
     n : a whipsnake of southern United States and Mexico; tail
         resembles a braided whip [syn: {coachwhip}, {Masticophis
         flagellum}]