Not, in itself, the whole caboodle? (3)
I believe the answer is:
kit
'not in' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for kit that I've seen before include "In strip" , "Necessary equipment" , "Specialised clothing or set of parts for assembly" , "Set of parts sold to be assembled" , "Equipment, clothing" .)