Wildly celebrating a hen or equivalent (15)
I believe the answer is:
interchangeable
'equivalent' is the definition.
(thesaurus)
'wildly celebrating a hen' is the wordplay.
'wildly' is an anagram indicator.
'celebrating'+'a'+'hen'='celebratingahen'
'celebratingahen' is an anagram of 'INTERCHANGEABLE'.
'or' is the link.
(Other definitions for interchangeable that I've seen before include "that can be traded in places" , "(Of things) that may be swapped over" .)