Monk has no resistance to plague (6)
I believe the answer is:
bother
'to plague' is the definition.
(thesaurus)
'monk has no resistance' is the wordplay.
'monk' becomes 'brother' (title for a monk).
'has no' suggests deleting specific letters.
'resistance' becomes 'r' (electronics abbreviation).
'brother' with 'r' removed is 'BOTHER'.
(Other definitions for bother that I've seen before include "Annoy or pester" , "Cause annoyance to, pester" , "Hassle - drat!" , "dash it!" , "Discommode, annoy" .)