Fairy godmother ultimately enveloped in rancour (6)
I believe the answer is:
sprite
'fairy' is the definition.
('sprite' can be a synonym of 'fairy')
'godmother ultimately enveloped in rancour' is the wordplay.
'ultimately' indicates one should take the final letters.
'enveloped in' indicates putting letters inside.
'rancour' becomes 'spite' (I've seen this before).
The last letter of 'godmother' is 'r'.
'r' inserted within 'spite' is 'SPRITE'.
(Other definitions for sprite that I've seen before include "Elf, fairy" , "sports car" , "Goblin, elf or imp" , "Puck, say" , "Impish type" .)