Ray, be quiet at the back! (5)
I believe the answer is:
shaft
'ray' is the definition.
(I know that ray can be written as shaft)
'quiet at the back' is the wordplay.
'quiet' becomes 'sh' (both can be said to tell someone to be quiet).
'at' means one lot of letters go next to another.
'the back' becomes 'aft' (at the back of a ship).
'sh'+'aft'='SHAFT'
'be' acts as a link.
(Other definitions for shaft that I've seen before include "Arrow part" , "Ray of light; spear" , "Beam - well" , "Arrow; vertical mine entrance" , "Vertical passage of mine" .)