Bumptious bat's foul brew (8)
I believe the answer is:
boastful
'bumptious' is the definition.
Both the definition and answer are adjectives. Maybe you can see a link between them that I don't see?
'bat's foul brew' is the wordplay.
'brew' indicates an anagram.
'bats'+'foul'='batsfoul'
'batsfoul' anagrammed gives 'BOASTFUL'.
Can you help me to learn more?
(Other definitions for boastful that I've seen before include "Vainglorious" , "Immodest" , "Talking with excessive pride in one's own ability" , "Given to bragging, being conceited" , "Given to blowing one's own trumpet" .)