Justify the rise of crude bombast (7)
I believe the answer is:
warrant
'justify' is the definition.
(synonyms)
'the rise of crude bombast' is the wordplay.
'the rise of' is a reversal indicator.
'crude' becomes 'raw' (synonyms).
'bombast' becomes 'rant' (synonyms).
'raw' backwards is 'war'.
'war'+'rant'='WARRANT'
(Other definitions for warrant that I've seen before include "Authorise, justify" , "Travel pass" , "Document giving authority" , "Guaranty - authorisation to make an arrest" , "Justify; authorisation" .)