A nun ordered a large yearbook (6)
I believe the answer is:
annual
'yearbook' is the definition.
('annual' can be a synonym of 'yearbook')
'a nun ordered a large' is the wordplay.
'ordered' indicates anagramming the letters.
'large' becomes 'l'.
'nun' anagrammed gives 'nnu'.
'a'+'nnu'+'a'+'l'='ANNUAL'
(Other definitions for annual that I've seen before include "plant > book" , "Reference book that's published every year" , "Twelve-monthly" , "Type of year book" , "Book; occurring once a year" .)