Snakes pass out (4)
I believe the answer is:
asps
'snakes' is the definition.
(asp is a kind of snake)
'pass out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'pass' with letters rearranged gives 'ASPS'.
(Other definitions for asps that I've seen before include "people" , "Pass around the snakes" , "poisonous things" , "Poplars" , "Poisonous creatures" .)