Like a piano given by singers including heartless tenor (6)
I believe the answer is:
strung
'like a piano' is the definition.
(a piano has strings or wires)
'given by singers including heartless tenor' is the wordplay.
'given by singers' becomes 'sung' (performed by singers).
'including' means one lot of letters goes inside another.
'heartless' means to remove the middle letters.
'tenor' with its centre removed is 'tr'.
'sung' placed around 'tr' is 'STRUNG'.
(Other definitions for strung that I've seen before include "(Of piano) given wires" , "Linked by" , "Threaded" , "suspended" , "tied up" .)