Outdoor celebration could be brief? No! (7)
I believe the answer is:
bonfire
'outdoor celebration' is the definition.
(I know that bonfire is a type of outdoor celebration)
'could be brief? no' is the wordplay.
'could be' indicates anagramming the letters.
'brief'+'no'='briefno'
'briefno' anagrammed gives 'BONFIRE'.
(Other definitions for bonfire that I've seen before include "The - of the Vanities (Tom Wolfe)" , "Source of blazing" , "If Ron be outside, is he alight?" , "lit up in the garden" , "Guy Fawkes Night blaze" .)