Leaders enduring long, extensive grief yell mournful song (5)
I believe the answer is:
elegy
'mournful song' is the definition.
(I've seen this in another clue)
'leaders enduring long extensive grief yell' is the wordplay.
'leaders' suggests taking the first letters.
The first letters of 'enduring long extensive grief yell' is 'ELEGY'.
(Other definitions for elegy that I've seen before include "Mournful poem, lament" , "Sad or reflective poem" , "Poetic lament (in a country churchyard?)" , "Poetic lament for the dead" , "that may be on the dead" .)