American priest secreted small insect (5)
I believe the answer is:
aphid
'small insect' is the definition.
(I've seen this before)
'american priest secreted' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'priest' becomes 'p' (ecclesiastical abbreviation).
'secreted' becomes 'hid' (I've seen this in another clue).
'a'+'p'+'hid'='APHID'
(Other definitions for aphid that I've seen before include "Plant louse" , "one living on juices" , "Greenfly etc" , "Horticultural pest" , "Small plant-sucking insect" .)