1 to say something in a loud whisper:
'Get out!' she hissed furiously
hiss at
She hissed at me to be quiet.

2 to make noise wich sounds like 'ssss':
The cat baked away, hissing.
Snakes only hiss when they are afraid.

3 if a crowd hisses a speaker, they interrupt them with angry sounds to show that they do not like them:
He was booed and hissed during a stormy meeting
- hiss noun [countable]
She heard a faint hiss a the metal struck the weather.