Absolute hush, always (5)
I believe the answer is:
sheer
'absolute' is the definition.
(I know that absolute can be written as sheer)
'hush always' is the wordplay.
'hush' becomes 'sh' (both are used to tell someone to be quiet).
'always' becomes 'eer' (poetic way of saying ever).
'sh'+'eer'='SHEER'
(Other definitions for sheer that I've seen before include "transparent fabric" , "Very fine like silk stockings" , "Film" , "Utter - precipitous" , "Plumb" .)