Paper around large field (5)
I believe the answer is:
realm
'field' is the definition.
(synonyms)
'paper around large' is the wordplay.
'paper' becomes 'ream' (a ream is an amount of paper).
'around' indicates putting letters inside.
'large' becomes 'L' (eg in clothes sizes).
'ream' enclosing 'l' is 'REALM'.
(Other definitions for realm that I've seen before include "Kingdom, domain" , "Area of knowledge under discussion" , "field of study" , "Kingdom could be lamer" , "where ruler holds sway?" .)