Dreadful alternative to a musical (10)

I believe the answer is:

calamitous

'dreadful' is the definition.
(thesaurus)

'alternative to a musical' is the wordplay.
'alternative' indicates anagramming the letters.
'to'+'a'+'musical'='toamusical'
'toamusical' with letters rearranged gives 'CALAMITOUS'.

(Another definition for calamitous that I've seen is " Catastrophic".)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.