Nobleman expected to throttle king (4)
I believe the answer is:
duke
'nobleman' is the definition.
(duke is a kind of nobleman)
'expected to throttle king' is the wordplay.
'expected' becomes 'due' (similar in meaning).
'to throttle' means one lot of letters goes inside another (throttle can mean to strangle or smother).
'king' becomes 'k' (abbreviation for king in chess).
'due' going around 'k' is 'DUKE'.
(Other definitions for duke that I've seen before include "Lord" , "Highest-ranking nobleman" , "Highest rank of British peer" , "Member of the nobility" , "Nobleman of the highest rank" .)