A do singer ruined being bombastic (9)
I believe the answer is:
grandiose
'bombastic' is the definition.
(I've seen this before)
'a do singer ruined' is the wordplay.
'ruined' is an anagram indicator.
'a'+'do'+'singer'='adosinger'
'adosinger' anagrammed gives 'GRANDIOSE'.
'being' is the link.
(Other definitions for grandiose that I've seen before include "Pretentiously imposing -- organised (anag)" , "Planned on a magnificent scale" , "Pretentiously impressive" , "Pretentiously magnificent" , "Impressive, magnificent" .)