The Collaborative International Dictionary of English v.0.48:
Horselaugh \Horse"laugh`\, n. A loud, boisterous laugh; a guffaw. --Pope. [1913 Webster]WordNet (r) 3.0 (2006):
horselaugh n 1: a loud laugh that sounds like a horse neighing [syn: hee- haw, horselaugh, ha-ha, haw-haw]