What's black chess piece (not king) (5)
I believe the answer is:
night
'what's black' is the definition.
(night can mean as black as night)
'chess piece not king' is the wordplay.
'chess piece' becomes 'knight' (knight is a type of chess piece).
'not' 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 "Hours of darkness" , "Dark hours" , "'The 2 8 of the dog in the _____'" , "Time for bed" , "'Red sky at . . . . ., shepherd's delight'" .)