Lament backing electronic network (5)
I believe the answer is:
dirge
'lament' is the definition.
('dirge' can be a synonym of 'lament')
'backing electronic network' is the wordplay.
'backing' says the letters should be written backwards.
'electronic' becomes 'e' (as in e-mail or e-books).
'network' becomes 'grid' (grid is a kind of network).
'e'+'grid'='egrid'
'egrid' in reverse letter order is 'DIRGE'.
(Other definitions for dirge that I've seen before include "dreary tune" , "Funereal music" , "Sombre music" , "Mournful chant" , "Funereal hymn" .)