Fail quickly, overlooking original grandiloquence (7)
I believe the answer is:
bombast
'grandiloquence' is the definition.
(I know that bombast is a type of grandiloquence)
'fail quickly overlooking original' is the wordplay.
'fail' becomes 'bomb' (synonyms).
'quickly overlooking original' becomes 'ast' (I can't explain this - if you can you should believe this answer much more).
'bomb'+'ast'='BOMBAST'
Can you help me to learn more?
(Other definitions for bombast that I've seen before include "hollow material" , "Pomposity" , "High-sounding words with little meaning" , "Pompous talk" , "High-sounding language with little meaning" .)