Much valuable material in the theatre a sure thing (8)
I believe the answer is:
treasure
'much valuable material' is the definition.
'treasure' can be an answer for 'material' (thesaurus). I'm not sure about the 'much valuable' bit.
'in the theatre a sure thing' is the wordplay.
'in' indicates a hidden word.
'TREASURE' is hidden within 'theatre a sure thing'.
Can you help me to learn more?
(Other definitions for treasure that I've seen before include "Classic adventure story" , "A collection of precious things" , "Hold dearly, like buried gold etc" , "Highly valued possession" , "Set great store by" .)