Act the blowhard (4)
I believe the answer is:
brag
'act the blowhard' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for brag that I've seen before include "'Show off, boast (4)'" , "Blow one's own trumpet" , "popular with 15 [EGOTIST] , no doubt" , "Boast, exaggerate" , "Idle talk" .)