Dark chesspiece hiding King (5)
I believe the answer is:
night
'dark' is the definition.
(it's dark at nighttime)
'chesspiece hiding king' is the wordplay.
'chesspiece' becomes 'knight' (I've seen this before).
'hiding' suggests deleting specific letters.
'king' becomes 'K' (abbreviation for king in chess).
'knight' with 'k' taken out is 'NIGHT'.
(Other definitions for night that I've seen before include "Time of darkness" , "Time without 10" , "Evening" , "''Twas the ... before Christmas, when all through the house / Not a creature was stirring, not even a mouse''" , "The dark time" .)