Source : Webster's Revised Unabridged Dictionary (1913)

Horselaugh \Horse"laugh`\, n.
   A loud, boisterous laugh; a guffaw. --Pope.

Source : WordNet®

horselaugh
     n : a loud laugh that sounds like a horse neighing [syn: {hee-haw},
          {ha-ha}, {haw-haw}]