Halt notes oddly for sad songs (7)
I believe the answer is:
laments
'sad songs' is the definition.
(I've seen this before)
'halt notes oddly' is the wordplay.
'halt' becomes 'lame' ('lame' can be a synonym of 'halt').
'oddly' means one should take alternating letters.
The alternating letters of 'notes' are 'nts'.
'lame'+'nts'='LAMENTS'
'for' acts as a link.
(Other definitions for laments that I've seen before include "Bewails" , "Mourns" , "elegies" , "Feels regret" , "Bemoans" .)