Disengage charge-carrying conductor’s base (4)
I believe the answer is:
free
'disengage' is the definition.
(synonyms)
'charge-carrying conductor's base' is the wordplay.
'charge' becomes 'fee' (fee is a kind of charge).
'carrying' indicates putting letters inside.
'conductor's base' becomes 'r' (I can't justify this - if you can you should give a lot more credence to this answer).
'fee' going around 'r' is 'FREE'.
Can you help me to learn more?
(Other definitions for free that I've seen before include "Pro bono" , "unemployed" , "Allowed to do as one pleases" , "At large" , "Let loose" .)