Shade obscures tail of flying monster (4)
I believe the answer is:
huge
'monster' is the definition.
(I've seen this in another clue)
'shade obscures tail of flying' is the wordplay.
'shade' becomes 'hue' (both can mean a colour).
'obscures' indicates putting letters inside (hides by surrounding with).
'tail of' says to take the final letters.
The last letter of 'flying' is 'g'.
'hue' placed around 'g' is 'HUGE'.
(Other definitions for huge that I've seen before include "Massive" , "Gigantic" , "Jumbo" , "Vast; immense" , "Colossal" .)