Pixie king stops malice (6)
I believe the answer is:
sprite
'pixie' is the definition.
(I've seen this before)
'king stops malice' is the wordplay.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'stops' means one lot of letters goes inside another.
'malice' becomes 'spite' (synonyms).
'r' put into 'spite' is 'SPRITE'.
(Other definitions for sprite that I've seen before include "Puck, say" , "Supernatural being" , "water pixie" , "Stripe on a fairy" , "Dainty type" .)