Clergyman overlooking last page (5)
I believe the answer is:
recto
'page' is the definition.
(right-hand page of an open book)
'clergyman overlooking last' is the wordplay.
'clergyman' becomes 'rector' (rector is a kind of clergyman).
'overlooking last' means to remove the last letter.
'rector' with its last letter removed is 'RECTO'.
(Other definitions for recto that I've seen before include "Side of paper" , "right page" , "Page three, for example" , "No leaves left" , "one side" .)