Cabaret singer ends poorly in quaver (5)
I believe the answer is:
trill
'quaver' is the definition.
('trill' can be a synonym of 'quaver')
'cabaret singer ends poorly' is the wordplay.
'ends' indicates one should take the final letters.
'poorly' becomes 'ill' ('ill' can be a synonym of 'poorly').
The last letters of 'cabaret singer' are 'tr'.
'tr'+'ill'='TRILL'
'in' acts as a link.
(Other definitions for trill that I've seen before include "Shake" , "High-pitched warbling sound" , "Warbling sound made by a songbird" , "Ornament" , "Rapid alternation of notes" .)