Each time, special grub (4)
I believe the answer is:
eats
'grub' is the definition.
('eats' can be a synonym of 'grub')
'each time special' is the wordplay.
'each' becomes 'ea'.
'time' becomes 't'.
'special' becomes 's' (common abbreviation as in Special Air Service).
'ea'+'t'+'s'='EATS'
(Other definitions for eats that I've seen before include "Food (slang)" , "fare" , "Common grub" , "Provisions" , "Commonly, they eliminate" .)