In regular bar not quite drunk? That's momentous? (8)
I believe the answer is:
eventful
'momentous?' is the definition.
(I've seen this in another clue)
'in regular bar not quite drunk?' is the wordplay.
'in regular bar' becomes 'event' (I can't justify this - if you can you should believe this answer much more).
'not quite' means to remove the last letter.
'drunk?' becomes 'full' (full can mean drunk in Australian slang).
'full' with its final letter removed is 'ful'.
'event'+'ful'='EVENTFUL'
'that's' is the link.
Can you help me to learn more?
(Other definitions for eventful that I've seen before include "Notable, full of incidents" , "Full of incidents, momentous" , "Lively and exciting" , "Packed with action, lots happening" , "Memorable; momentous" .)