Self-satisfied sergeant major outwardly unappealing (4)
I believe the answer is:
smug
'self-satisfied' is the definition.
(synonyms)
'sergeant major outwardly unappealing' is the wordplay.
'sergeant major' becomes 'SM' (abbreviation for sergeant major).
'outwardly' says to hollow out the word (remove centre letters) (only the outermost letters are used).
'unappealing' with its centre taken out is 'ug'.
'sm'+'ug'='SMUG'
(Other definitions for smug that I've seen before include "Self-satisfied, stuffy" , "Unctuous" , "Showing excessive self-pride" , "Smirking" , "Full of oneself" .)