Party I'd organised for excursion (3,4)
I believe the answer is:
day trip
'excursion' is the definition.
(I've seen this before)
'party i'd organised' is the wordplay.
'organised' indicates anagramming the letters.
'party'+'id'='partyid'
'partyid' with letters rearranged gives 'DAY TRIP'.
'for' acts as a link.
(Other definitions for day trip that I've seen before include "Brief excursion" , "Excursion within 24 hours" , "Pay dirt (anag.)" , "Outing" .)