Squirrel snack (5)
I believe the answer is:
acorn
'squirrel snack' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for acorn that I've seen before include "Fruit-seed of the oak" , "mast" , "Nut of oak tree" , "Oak seed" , "cup's content" .)