Siren yet to disturb peace (8)
I believe the answer is:
serenity
'peace' is the definition.
(I know that peace can be written as serenity)
'siren yet to disturb' is the wordplay.
'to disturb' is an anagram indicator (I've seen 'disturbing' mean this).
'siren'+'yet'='sirenyet'
'sirenyet' is an anagram of 'SERENITY'.
(Other definitions for serenity that I've seen before include "Calm composure, peace" , "Peace and quiet" , "Peacefulness" , "Peace, tranquillity" , "Tiny seer in state of repose" .)