Sad song about ridge being lost (5)
I believe the answer is:
dirge
'sad song' is the definition.
(I've seen this in another clue)
'ridge being lost' is the wordplay.
'being lost' indicates anagramming the letters.
'ridge' anagrammed gives 'DIRGE'.
'about' is the link.
(Other definitions for dirge that I've seen before include "Requiem" , "Lamentation" , "feature of funeral" , "Funeral music" , "dreary tune" .)