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2 definitions by Rachael and Nicole.

 
1.
The act of making a wheezing noise while laughing.
"OMG! what you just said, made me laugh so hard i started HISSSing! HISSSSSSSS!"
by Rachael and Nicole. July 27, 2008
 
2.
The act of laughing so hard in a public quiet place, that you have to put your head down in your arms so no one hears you. Sometimes you laugh so hard you hisss
my friend texted me a joke and i modi in public.
by Rachael and Nicole. July 27, 2008