Puccini opera (5)
I believe the answer is:
'puccini opera' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tosca that I've seen before include "Puccini's Rome opera" , "Luigi -, Italian playwright" , "Puccini's jumper" , "Puccini's Roman heroine" , "18 [OPERA]" .)