After reflecting hard, tweet some sudden revelation (8)
I believe the answer is:
epiphany
'sudden revelation' is the definition.
(I've seen this before)
'after reflecting hard tweet some' is the wordplay.
'after reflecting' says the letters should be written backwards.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'tweet' becomes 'pipe' (both can mean to make a high-pitched sound).
'some' becomes 'any' (similar in meaning).
'h'+'pipe'='hpipe'
'hpipe' reversed gives 'epiph'.
'epiph'+'any'='EPIPHANY'
(Other definitions for epiphany that I've seen before include "Festival commemorating the showing of Christ to the Magi" , "Church festival" , "Moment of sudden revelation (involving three wise men from the east?)" , "Sudden realisation" , "when the wise men bring gifts" .)