Swollen-headed (4)
I believe the answer is:
vain
'swollen-headed' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for vain that I've seen before include "Conceited - futile" , "Conceited, proud of appearance" , "Having an exaggerated sense of self-importance" , "Conceited, arrogant" , "Conceited and ineffectual" .)