One who delivers stick up on isle (7)
I believe the answer is:
postman
'one who' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'stick up on isle' is the wordplay.
'stick up' becomes 'post' (as in posting a notice in public).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'isle' becomes 'man' (the Isle of Man is an example).
'post'+'man'='POSTMAN'
'delivers' acts as a link.
Can you help me to learn more?
(Other definitions for postman that I've seen before include "Male mail carrier" , "Letter deliverer" , "Male to deliver mail" , "Chap with letters" , "TV's Pat, for instance" .)