Source of wool leggings initially adopted by priest (5)
I believe the answer is:
llama
'source of wool' is the definition.
(I've seen this before)
'leggings initially adopted by priest' is the wordplay.
'initially' says to take the initial letters.
'adopted by' is an insertion indicator (I've seen this in other clues).
'priest' becomes 'lama' (lama is a kind of priest).
The initial letter of 'leggings' is 'l'.
'l' going into 'lama' is 'LLAMA'.
(Other definitions for llama that I've seen before include "Woolly Andean animal" , "Load-carrier" , "Andean 'camel'" , "Woollen cloth" , "Peruvian transportation" .)