Boasting about a number well done (7)
I believe the answer is:
bravado
'boasting' is the definition.
(thesaurus)
'about a number well done' is the wordplay.
'about' means one lot of letters goes inside another.
'number' becomes 'd' (D is an example**).
'well done' becomes 'bravo' (I've seen this before).
'a'+'d'='ad'
'ad' put inside 'bravo' is 'BRAVADO'.
(Other definitions for bravado that I've seen before include "great self-confidence" , "Swaggering show of boldness" , "Bottle" , "Swaggering show of false courage" , "A show of boldness or bluster" .)