Alarm bell (6)
I believe the answer is:
tocsin
'alarm bell' is the definition.
(I know that alarm bell can be written as tocsin)
This is the entire clue.
(Other definitions for tocsin that I've seen before include "Alarm bell to be found in Scot" , "An alarm bell or signal" , "The sound of an alarm bell" , "alarm call" , "Con, sit and produce an alarmbell" .)