Daggers bishop plunged into old priest (5)
I believe the answer is:
obeli
'daggers' is the definition.
(I've seen this before)
'bishop plunged into old priest' is the wordplay.
'bishop' becomes 'B' (chess abbreviation).
'plunged into' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'priest' becomes 'eli' (biblical figure).
'o'+'eli'='oeli'
'b' going within 'oeli' is 'OBELI'.
(Other definitions for obeli that I've seen before include "signs of doubt" , "Dagger-shaped signs" , "Dagger signs for footnotes" , "Signs of death" , "daggers drawn" .)