Grandiose wine at bottom of tank cold (9)
I believe the answer is:
bombastic
'grandiose' is the definition.
(thesaurus)
'wine at bottom of tank cold' is the wordplay.
'wine' becomes 'asti' (Italian wine).
'at bottom of' says to put letters next to each other (in a down clue, some letters go underneath others).
'tank' becomes 'bomb' (I've seen this in another clue).
'cold' becomes 'C' (eg on taps).
'asti' put after 'bomb' is 'bombasti'.
'bombasti'+'c'='BOMBASTIC'
(Other definitions for bombastic that I've seen before include "I cast bomb, being pompous in speech" , "affected" , "Declamatory, ostentatiously lofty" , "Extravagant" , "Pretentious" .)