Nip the nipper (3)
I believe the answer is:
tot
'nipper' is the definition.
(tot is a kind of nipper)
'nip the' is the wordplay.
'nip' becomes 'to' (I can't justify this - if you can you should believe this answer much more).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'to'+'t'='TOT'
Can you help me to learn more?
(Other definitions for tot that I've seen before include "slug?" , "A wee dram" , "Youngster; short drink" , "Small measure for a small child" , "Child; measure of spirits" .)