A hush, back in the mine (5)
I believe the answer is:
shaft
'mine' is the definition.
(thesaurus)
'a hush back' is the wordplay.
'a hush' becomes 'sh'.
'back' becomes 'aft' ('aft' is associated in meaning with 'back'**).
'sh'+'aft'='SHAFT'
'in the' is the link.
(Other definitions for shaft that I've seen before include "Body of an arrow" , "Vertical passage of mine" , "Ray (of sunlight)" , "A little light" , "Long slender part or deep vertical opening" .)