Questionable to supply shortened sung performance (9)
I believe the answer is:
equivocal
'questionable' is the definition.
(similar in meaning)
'supply shortened sung performance' is the wordplay.
'supply' becomes 'equip' (equipping is a kind of supplying).
'shortened' means to remove the last letter.
'sung performance' becomes 'vocal' (I can't explain this - if you can you should believe this answer much more).
'equip' with its last letter removed is 'equi'.
'equi'+'vocal'='EQUIVOCAL'
'to' is the link.
Can you help me to learn more?
(Other definitions for equivocal that I've seen before include "Dithering, evasive" , "Questionable" , "suspicious" , "uncertain" , "it's indefinite" .)