Formation of Eastern church Noel arranged (7)
I believe the answer is:
echelon
'formation' is the definition.
(I've seen this before)
'eastern church noel arranged' is the wordplay.
'eastern' becomes 'e'.
'church' becomes 'ch' (common abbreviation).
'arranged' is an anagram indicator.
'noel' with letters rearranged gives 'elon'.
'e'+'ch'+'elon'='ECHELON'
'of' acts as a link.
(Other definitions for echelon that I've seen before include "Military stepped formation" , "Body of troops arranged in a line" , "Ladder formation" , "Level or rank in a group" , "Leech on (anag.)" .)