Hush nieces playing round lake (7)
I believe the answer is:
silence
'hush' is the definition.
(I know that hush can be written as silence)
'nieces playing round lake' is the wordplay.
'playing' is an anagram indicator.
'round' means one lot of letters goes inside another.
'lake' becomes 'L' (geographical abbreviation).
'nieces' is an anagram of 'sience'.
'sience' placed around 'l' is 'SILENCE'.
(Other definitions for silence that I've seen before include "No talking" , "Nothing said" , "What's left of burnt coal" , "Noiselessness" , "License (anag)" .)