Lament ridge being lost (5)
I believe the answer is:
dirge
'lament' is the definition.
(synonyms)
'ridge being lost' is the wordplay.
'being lost' indicates anagramming the letters.
'ridge' anagrammed gives 'DIRGE'.
(Other definitions for dirge that I've seen before include "Funeral hymn" , "Threnody" , "Dreary song" , "dreary tune" , "Funeral music" .)