Fool around next to big hole (5)
I believe the answer is:
abyss
'big hole' is the definition.
(an abyss is a large chasm or pit)
'fool around next to' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'around' is an insertion indicator.
'next to' becomes 'by'.
'ass' going around 'by' is 'ABYSS'.
(Other definitions for abyss that I've seen before include "Deep gulf" , "something rather deep" , "gaping hole" , "depths of sea" , "Bottomless gulf" .)