Annual Fourth of July opening (6)
I believe the answer is:
yearly
'annual' is the definition.
(I know that annual can be written as yearly)
'fourth of july opening' is the wordplay.
'fourth of july' becomes 'y' (fourth letter of the word 'July').
'opening' becomes 'early' (I've seen this before).
'y'+'early'='YEARLY'
(Other definitions for yearly that I've seen before include "Perennial" , "on a regular basis" , "At annual intervals" , "Happening every twelve months" , "Approximately every 52 weeks" .)