English drunk in happy moment of revelation (8)
I believe the answer is:
epiphany
'moment of revelation' is the definition.
(an epiphany is a revelation)
'english drunk in happy' is the wordplay.
'english' becomes 'e' (abbreviation).
'drunk' is an anagram indicator.
'in'+'happy'='inhappy'
'inhappy' with letters rearranged gives 'piphany'.
'e'+'piphany'='EPIPHANY'
(Other definitions for epiphany that I've seen before include "Church festival" , "Its events occur in Matthew" , "Sudden realisation" , "Festival commemorating the showing of Christ to the Magi" , "Christian Festival, showing of Christ to the Magi" .)