Inadequate hatless uncle (6)
I believe the answer is:
lender
'uncle' is the definition.
(informal term for a pawnbroker)
'inadequate hatless' is the wordplay.
'inadequate' becomes 'slender' (I've seen this before).
'hatless' means to remove the first letter (the hat of the word is its first letter).
'slender' with its initial letter taken off is 'LENDER'.
(Other definitions for lender that I've seen before include "Provider of a loan" , "One making advances" , "Neither a borrower nor a ... be, it's said" , "One gives credit" , "Bank or building society" .)