Priest in church finds artefact (5)
I believe the answer is:
relic
'artefact' is the definition.
(I've seen this before)
'priest in church' is the wordplay.
'priest' becomes 'eli' (biblical figure).
'in' means one lot of letters goes inside another.
'church' becomes 'rc' (abbreviation for Roman Catholic).
'eli' put into 'rc' is 'RELIC'.
'finds' is the link.
(Other definitions for relic that I've seen before include "Trace" , "Ossified survival" , "precious object" , "Fossil" , "Object from antiquity" .)