Worn out piano delivered outside (5)
I believe the answer is:
spent
'worn out' is the definition.
(I know this)
'piano delivered outside' is the wordplay.
'piano' becomes 'p' (musical abbreviation).
'delivered' becomes 'sent' (I've seen this in another clue).
'outside' means one lot of letters goes inside another.
'p' inserted into 'sent' is 'SPENT'.
(Other definitions for spent that I've seen before include "Used up; exhausted" , "Splashed out" , "Expended" , "Completely exhausted" , "Exhausted, having paid money?" .)