Wisdom, perhaps, but not an average amount (4)
I believe the answer is:
norm
'an average amount' is the definition.
(I've seen this in another clue)
'wisdom perhaps but not' is the wordplay.
I cannot quite see how this works, but
'not' could be 'no' (negative) and 'no' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for norm that I've seen before include "Standard amount or customary behaviour" , "Average result" , "Something typical" , "Rule; average" , "(The) accepted way" .)