Experimental musical mounted under marquee for example (9)
I believe the answer is:
tentative
'experimental' is the definition.
(tentative can mean experimental or exploratory)
'musical mounted under marquee for example' is the wordplay.
'musical' becomes 'evita' (Andrew Lloyd Webber musical).
'mounted' says the letters should be written backwards.
'under' means one lot of letters go next to another.
'marquee for example' becomes 'tent' (marquee is a kind of tent).
'evita' written backwards gives 'ative'.
'ative' after 'tent' is 'TENTATIVE'.
(Other definitions for tentative that I've seen before include "Diffident" , "Conjectural" , "To be confirmed" , "Cautious - provisional" , "Exploratory - hesitant" .)