Quiet at the back of tunnel (5)
I believe the answer is:
shaft
'tunnel' is the definition.
(thesaurus)
'quiet at the back' is the wordplay.
'quiet' becomes 'sh' ('sh' is used to tell someone to be quiet).
'at' is a charade indicator (letters next to each other).
'the back' becomes 'aft' (I've seen this in other clues).
'sh'+'aft'='SHAFT'
'of' acts as a link.
(Other definitions for shaft that I've seen before include "Ray of light; treat unfairly" , "An arrow or a mine passage" , "Ray (of sunlight)" , "Long rod or column of light" , "Arrow part" .)