Outstanding musical composition for a pair in short (3)
I believe the answer is:
due
'outstanding' is the definition.
(an outstanding debt is due)
'pair in short' is the wordplay.
'pair' becomes 'duet' (synonyms).
'in short' means to remove the last letter.
'duet' with its final letter taken off is 'DUE'.
'musical composition for a' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for due that I've seen before include "Entitlement" , "Appropriate - fee - now owing" , "Unpaid or expected" , "imminent" , "deserts" .)