Unruffled church leader wearing tartan cloth (6)
I believe the answer is:
placid
'unruffled' is the definition.
('placid' can be a synonym of 'unruffled')
'church leader wearing tartan cloth' is the wordplay.
'leader' indicates taking the first letters.
'wearing' means one lot of letters goes inside another.
'tartan cloth' becomes 'plaid' (I've seen this before).
The first letter of 'church' is 'c'.
'c' put into 'plaid' is 'PLACID'.
(Other definitions for placid that I've seen before include "Tranquil, unruffled" , "without ruffles" , "Serene - unruffled" , "Not ruffled" , "Calm of nature" .)