Initiates of alphabetical jigsaw and Araucaria's Xmas Club (4)
I believe the answer is:
ajax
'club' is the definition.
(AFC Ajax are a Dutch football club)
'initiates of alphabetical jigsaw and araucaria's xmas' is the wordplay.
'initiates of' indicates taking the first letters (the letters which initiate the words).
'and' means one lot of letters go next to another.
'araucaria's xmas' becomes 'ax' (this might be a standard abbreviation of which I'm unaware).
The initial letters of 'alphabetical jigsaw' is 'aj'.
'aj'+'ax'='AJAX'
(Other definitions for ajax that I've seen before include "Greek warrior (Iliad)" , "eleven from the Netherlands" , "Ancient Greek hero" , "Legendary warrior" , "Greek hero of the Trojan War - Dutch soccer team" .)