Opera awkward to cast with only one tenor (5)
I believe the answer is:
tosca
'opera' is the definition.
(Giacomo Puccini opera)
'awkward to cast with only one tenor' is the wordplay.
I cannot quite see how this works, but
'to' is present in the answer.
'one' could be 'a' (a thing is one thing) and 'a' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for tosca that I've seen before include "One of Puccini's 19" , "opera singer" , "Puccini's Rome opera" , "musical work" , "Coats off for Pucccni's opera" .)