Talks big (6)
I believe the answer is:
boasts
'talks big' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for boasts that I've seen before include "Brags in praise of oneself" , "Brags, blows" , "crows" , "Brags, shows off" , "Blows one's own trumpet" .)