Priest stopping religious festival before mice spread an outbreak of the plague? (8)
I believe the answer is:
epidemic
'an outbreak of the plague?' is the definition.
(outbreak of disease)
'priest stopping religious festival before mice spread' is the wordplay.
'priest' becomes 'p' (ecclesiastical abbreviation).
'stopping' is an insertion indicator (stopping can mean blocking a gap).
'religious festival' becomes 'eid' (I've seen this before).
'before' means one lot of letters go next to another.
'spread' is an anagram indicator.
'p' going inside 'eid' is 'epid'.
'mice' is an anagram of 'emic'.
'epid'+'emic'='EPIDEMIC'
(Other definitions for epidemic that I've seen before include "Dim piece (anag)" , "Citrus fruit" , "Rash" , "Disease affecting many in a population at the same time" , "Fast food item" .)