Every last bit (3)
I believe the answer is:
all
'every last bit' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for all that I've seen before include "Comprising every individual one" , "The lot, everyone" , "Quite" , "100%" , "and 16 Across and 23 Across: Even so" .)