Fools pass out (4)
I believe the answer is:
saps
'fools' is the definition.
(I know this)
'pass out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'pass' with letters rearranged gives 'SAPS'.
(Other definitions for saps that I've seen before include "Pass around foolish people" , "Vital juices" , "More than one fool" , "trenches" , "Weakens, deprives of energy" .)