Daydreams about large celebrations (9)
I believe the answer is:
revelries
'celebrations' is the definition.
(revelry is a kind of celebration)
'daydreams about large' is the wordplay.
'daydreams' becomes 'reveries' ('revery' can be a synonym of 'daydream').
'about' is an insertion indicator.
'large' becomes 'l'.
'reveries' placed around 'l' is 'REVELRIES'.
(Other definitions for revelries that I've seen before include "Fantasies" , "Lively festivities" .)