Undercharge daughter for fuel (4)
I believe the answer is:
feed
'for fuel' is the definition.
(as in fuelling or feeding a fire)
'undercharge daughter' is the wordplay.
'undercharge' becomes 'fee' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'daughter' becomes 'd' (genealogical abbreviation).
'fee'+'d'='FEED'
Can you help me to learn more?
(Other definitions for feed that I've seen before include "Paid" , "comedian's assistant" , "Eat; pass (a ball) to another player" , "forage" , "Straight man" .)