Work for tenor in the role of king (4)
I believe the answer is:
task
'work' is the definition.
(I know that task is a type of duty)
'tenor in the role of king' is the wordplay.
'tenor' becomes 't'.
'in the role of' becomes 'as' (as in an actor appearing as a character).
'king' becomes 'K' (abbreviation for king in chess).
't'+'as'+'k'='TASK'
'for' acts as a link.
(Other definitions for task that I've seen before include "Job to be done" , "Chore, job." , "Piece of work to be done" , "Arduous bit of work" , "commission" .)