Not a bit of it! (6)
I believe the answer is:
entire
'it' is the definition.
The definition suggests a singular noun which matches the answer.
'not a bit' is the wordplay.
I cannot quite understand how this works, but
'not' could be 'nt' (synonyms) and 'nt' is present in the answer.
'bit' could be 'i' (resembles 1, a binary digit or bit) and 'i' is found in the answer.
The remaining letters 'ere' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for entire that I've seen before include "in one piece" , "Full and complete" , "Envelope" , "Lure" , "Whole; unbroken" .)