Manuscript found on lectern in Oxford, originally (5)
I believe the answer is:
folio
'manuscript' is the definition.
(I've seen this before)
'found on lectern in oxford originally' is the wordplay.
'originally' suggests taking the first letters.
The initial letters of 'found on lectern in oxford' is 'FOLIO'.
(Other definitions for folio that I've seen before include "large book" , "Book made of folded sheets" , "Two-leaf sheet" , "Leaf of book - page number" , "Sheet folded to form two leaves in book - page number" .)