Tosca pointlessly included singular musical composition (7)
I believe the answer is:
toccata
'musical composition' is the definition.
(toccata is a kind of musical composition)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for toccata that I've seen before include "Baroque musical piece" , "Series of musical runs and chords before a fugue" , "Musical composition with rapid elaborate runs" , "Musical composition for keyboard to show technique" , "Baroque musical composition" .)