sss

sss (with any number of S's to indicate duration)

1. (onomatopoeia) The hiss of a snake or other reptile.
   • 2017, Brian Fox, The Hollow Rasping of an American Nightmare, page 420:

     "Sss," said the snake.

sss

1. (mathematics, logic) if and only if; used to show that the predicate that follows it has the same truth value as the predicate that precedes it

• se