Keep tenor in reserve for last short piece (4)
I believe the answer is:
stub
'last short piece' is the definition.
(stub can mean the end piece of something)
'keep tenor in reserve' is the wordplay.
I cannot quite see how this works, but
'tenor' could be 't' and 't' is found in the answer.
'reserve' could be 'sub' (I've seen this in other clues) and 'sub' is found in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'for' acts as a link.
(Other definitions for stub that I've seen before include "Counterfoil, of a cheque say" , "Ticket counterfoil" , "Returned part of a ticket" , "Possible proof of journey" , "Short pencil remnant" .)