... let out polite word when removing cap (5)
I believe the answer is:
lease
'let' is the definition.
(as in to lease or let a building)
'polite word when removing cap' is the wordplay.
I cannot quite see how this works, but
'when' could be 'as' (eg 'when I walked' means 'as I walked') and 'as' is found in the answer.
The remaining letters 'lee' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'out' acts as a link.
Can you help me to learn more?
(Other definitions for lease that I've seen before include "Contract of tenure" , "Tenancy contract" , "Ghost" , "Summer's has too short a date (Shak.)" , "Contract allowing use of a property" .)