Piece of writing found in small underground chapel, reportedly (6)
I believe the answer is:
script
'piece of writing' is the definition.
(thesaurus)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for script that I've seen before include "Orginal document" , "Person preparing text for film actors" , "Form of writing" , "Piece of handwriting" , "Written form (of play etc)" .)