Nettle rash at first seen on priest from the east (4)
I believe the answer is:
rile
'nettle' is the definition.
('rile' can be a synonym of 'nettle')
'rash at first seen on priest from the east' is the wordplay.
'at first' says to take the initial letters.
'seen on' says to put letters next to each other.
'priest' becomes 'eli' (I've seen this before).
'from the east' is a reversal indicator.
The initial letter of 'rash' is 'r'.
'eli' backwards is 'ile'.
'r'+'ile'='RILE'
(Other definitions for rile that I've seen before include "'Vex, irritate (4)'" , "Lire (anag)" , "Irritate considerably" , "Stir up anger" , "Informally, annoy or irritate" .)