Fee provided by petty officer at part of journey (7)
I believe the answer is:
postage
'fee' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'petty officer at part of journey' is the wordplay.
'petty officer' becomes 'po' (naval abbreviation).
'at' is a charade indicator (letters next to each other).
'part of journey' becomes 'stage' ('stage' is part of 'journey').
'po'+'stage'='POSTAGE'
'provided by' is the link.
Can you help me to learn more?
(Other definitions for postage that I've seen before include "Money charged for delivery" , "It could be first-class" , "Cost to send a mail item" , "Delivery cost" , "Cost of sending letter" .)