Source : Webster's Revised Unabridged Dictionary (1913)

Horsewhip \Horse"whip`\, n.
   A whip for horses.

Horsewhip \Horse"whip`\, v. t.
   To flog or chastise with a horsewhip.

Source : WordNet®

horsewhip
     v : whip with a whip intended for horses
     [also: {horsewhipping}, {horsewhipped}]

horsewhip
     n : a whip for controlling horses
     [also: {horsewhipping}, {horsewhipped}]