Told colonel to eat it (3)
I believe the answer is:
nut
'it' is the definition.
The definition suggests a singular noun which matches the answer.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for nut that I've seen before include "buff" , "Hard-skinned fruit" , "keen admirer" , "Head (slang)" , "Hazel; beech" .)