Monk astride large pack animal (5)
I believe the answer is:
llama
'pack animal' is the definition.
(I've seen this before)
'monk astride large' is the wordplay.
'monk' becomes 'lama' (I've seen this before).
'astride' means one lot of letters goes inside another.
'large' becomes 'l'.
'lama' enclosing 'l' is 'LLAMA'.
(Other definitions for llama that I've seen before include "one to chew the cud" , "As bearer of burdens" , "Pack animal, native to the Andes" , "Andean pack animal" , "Long-necked woolly animal" .)