Gloating, small face (4)
I believe the answer is:
smug
'gloating small face' is the definition.
I can't judge whether this defines the answer.
'small face' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'face' becomes 'mug' (informal term for face).
's'+'mug'='SMUG'
Can you help me to learn more?
(Other definitions for smug that I've seen before include "looking pleased with itself" , "Unpleasantly complacent" , "Steal" , "Self-satisfied, complacent" , "Conceited and self-satisfied" .)