The Collaborative International Dictionary
hee-haw \hee-haw\ n. a loud laugh that sounds like a horse neighing.
Syn: horselaugh, ha-ha, haw-haw.
hee-haw \hee-haw\ v. i. to bray in the manner of a donkey.
Syn: bray.
Douglas Harper's Etymology Dictionary
also heehaw, first recorded 1815 (as Hiu Haw), probably imitative of sound of donkey's bray (compare French hinham). As "a loud laugh" from 1843.
Wiktionary
interj. The cry of an ass or donkey. n. 1 The cry of an ass or donkey. 2 (context Scotland slang English) nothing. vb. (context intransitive English) To utter the cry of an ass or donkey.
WordNet
n. a loud laugh that sounds like a horse neighing [syn: horselaugh, ha-ha, haw-haw]
v. braying characteristic of donkeys [syn: bray]
Usage examples of "hee-haw".
They hee-hawed and laughed, sputtered and chattered and babbled--a dozen cracked voices assassinated "Malaguefia Salerosa," jubilantly they murdered it up to the spider-webbed rafters and well beyond.
That could have been a reference to anything from Jimmy Carter's Iran policy to Bill Clinton's intern policy to Hee-Haw reruns.