Entertained by sheikh, a king is something drab (5)
I believe the answer is:
khaki
'drab' is the definition.
(I have seen 'Olive drab ' mean 'khaki' so perhaps 'drab' could also mean 'khaki')
'entertained by sheikh a king is something' is the wordplay.
'entertained by' says the answer is hidden in the clue.
'KHAKI' is hidden within 'sheikh a king something'.
(Other definitions for khaki that I've seen before include "Military fabric" , "'Colour, often used for military uniforms (5)'" , "Army fabric" , "Yellowish brown colour" , "Drably coloured" .)