Noiselessness (7)
I believe the answer is:
silence
'noiselessness' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for silence that I've seen before include "It is golden, they say" , "'The rest is - - '(Hamlet)" , "There's nothing heard" , "Period of peace" , "Absence of racket" .)