Serpents pass out (4)
I believe the answer is:
asps
'serpents' is the definition.
(asp is a kind of serpent)
'pass out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'pass' anagrammed gives 'ASPS'.
(Other definitions for asps that I've seen before include "Poisonous snakes" , "Small vipers" , "Poisonous creepers" , "because of their venom?" , "Cleopatra's snakes" .)