Amount put up to house a grand priest (5)
I believe the answer is:
magus
'priest' is the definition.
(magus is a kind of priest)
'amount put up to house a grand' is the wordplay.
'amount' becomes 'sum' (synonyms).
'put up' says the letters should be written in reverse.
'to house' means one lot of letters goes inside another.
'grand' becomes 'G' (G is short for ground as in a thousand).
'sum' backwards is 'mus'.
'a'+'g'='ag'
'mus' placed around 'ag' is 'MAGUS'.
(Other definitions for magus that I've seen before include "Priest" , "eg Melchior" , "astrologer" , "Sorcerer" , "Magician, wise man" .)