Printing type used for the first prayer book? (6)
I believe the answer is:
primer
'book?' is the definition.
(primer is a kind of book)
'printing type used for the first prayer' is the wordplay.
I cannot quite see how this works, but
'first' could be 'prime' (similar in meaning) and 'prime' is found within the answer.
A single letter 'r' 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 primer that I've seen before include "Initial coat of paint" , "Solitary" , "First school book" , "Basic book; undercoat" , "School textbook" .)