The boaster's bloomer (5)
I believe the answer is:
aster
'bloomer' is the definition.
(I know that aster is a type of bloomer)
'the boaster's' is the wordplay.
'ASTER' is hidden within the letters.
However, I'm uncertain how this is indicated.
Can you help me to learn more?
(Other definitions for aster that I've seen before include "Plant of Michaelmas daisy family" , "Plant like a Michaelmas daisy" , "Purple pink flowered plant" , "eg Michaelmas daisy" , "Daisy-like plant" .)