Skim milk's lack (3)
I believe the answer is:
fat
'skim milk's lack' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for fat that I've seen before include "and 24: Overpaid City type" , "Naturally oily substance" , "eg Lard" , "Adipose tissue" , "Corpulent; little (chance)" .)