Noble expected to shelter monarch (4)
I believe the answer is:
duke
'noble' is the definition.
(I know that duke is a type of noble)
'expected to shelter monarch' is the wordplay.
'expected' becomes 'due' (similar in meaning).
'to shelter' is an insertion indicator.
'monarch' becomes 'k' (abbreviation for king in chess).
'due' placed around 'k' is 'DUKE'.
(Other definitions for duke that I've seen before include "Nobleman - fist" , "Fist (sl.)" , "High hereditary title in Britain" , "Highest ranked British peer" , "Highest hereditary title in Britain" .)