Fool securing Times opening (5)
I believe the answer is:
abyss
'opening' is the definition.
(term for a void or gap)
'fool securing times' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'securing' indicates putting letters inside.
'times' becomes 'by' (both can mean 'multiplied by').
'ass' enclosing 'by' is 'ABYSS'.
(Other definitions for abyss that I've seen before include "canyon?" , "crevasse" , "Hell; hole" , "Bottomless pit" , "depths of sea" .)