Ultimate characters seen in the magnificent Coptic church make an impression (4)
I believe the answer is:
etch
'make an impression' is the definition.
(to etch is to make an impression in something)
'ultimate characters seen in the magnificent coptic church' is the wordplay.
I cannot quite see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found within the answer.
'church' could be 'ch' (common abbreviation) and 'ch' is found within the answer.
A single letter 'e' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for etch that I've seen before include "Inscribe" , "Make incisions" , "Carve into surface, impress deeply" , "Cut using sharp instrument" , "Cut design onto metal using acid" .)