One cast as 'Diane East'? (3)
I believe the answer is:
die
'one cast' is the definition.
(thesaurus)
''diane east'?' is the wordplay.
''diane' becomes 'di' (short for Diane).
'east'?' becomes 'e' (abbreviation).
'di'+'e'='DIE'
'as' acts as a link.
(Other definitions for die that I've seen before include "THIRD PART OF 24" , "Mould; become extinct" , "a block?" , "one proverbially straight" , "Cube with spots on the six faces" .)