Haw-haw (h&asuml_;h&asuml_;), n. [Duplication of haw a hedge.] 1. See Ha-ha.
[1913 Webster]

2. a loud laugh that sounds like a horse neighing. [wns=1]
Syn. -- hee-haw, horselaugh, ha-ha.
[WordNet 1.5]

3. a sunken fence (so as not to interfere with the view). [wns=3]
Syn. -- haha.
[WordNet 1.5]