Mournful sound (5)
I believe the answer is:
knell
'mournful sound' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for knell that I've seen before include "it precipitates death" , "Funeral toll" , "Awesome ring" , "Toll (bell)" , "Solemnly proclaim death" .)