Maybe sly about a bit of a fib, the witch! (5)
I believe the answer is:
sibyl
'witch' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'maybe sly about a bit of a fib' is the wordplay.
'maybe' indicates an anagram.
'about' means one lot of letters goes inside another.
'a bit of a fib' becomes 'ib' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'sly' is an anagram of 'syl'.
'syl' enclosing 'ib' is 'SIBYL'.
'the' is the link.
Can you help me to learn more?
(Other definitions for sibyl that I've seen before include "Ancient Roman prophetess" , "Ancient seer - prophetess" , "Greek prophetess" , "Charmer" , "Woman mouthpiece of a god, uttering prophecies" .)