Is return fast and quiet? (6)
I believe the answer is:
silent
'quiet?' is the definition.
('silent' can be similar in meaning to 'quiet')
'is return fast' is the wordplay.
'return' says the letters should be written backwards.
'fast' becomes 'lent' (I've seen this before).
'is' back-to-front is 'si'.
'si'+'lent'='SILENT'
'and' acts as a link.
(Other definitions for silent that I've seen before include "unable to speak?" , "Mute" , "Strange and astonishing thing" , "Enlist (anag) - mum" , "Unspeaking" .)