Quiet nieces first to leave in confusion (7)
I believe the answer is:
silence
'quiet' is the definition.
(I know that quiet can be written as silence)
'nieces first to leave in confusion' is the wordplay.
'first to' indicates taking the first letters.
'in confusion' indicates an anagram.
The first letter of 'leave' is 'l'.
'nieces'+'l'='niecesl'
'niecesl' anagrammed gives 'SILENCE'.
(Other definitions for silence that I've seen before include "Quietness" , "may be required in court" , "Noiselessness" , "that's golden" , "It is said to be golden" .)