Page, reserved initially, I am finding formal (4)
I believe the answer is:
prim
'formal' is the definition.
(thesaurus)
'page reserved initially i am' is the wordplay.
'initially' says to take the initial letters.
'i am' becomes 'im'.
The first letters of 'page reserved' is 'pr'.
'pr'+'im'='PRIM'
'finding' acts as a link.
(Other definitions for prim that I've seen before include "Prudish, formal" , "Formally prudish" , "Stiffly formal and proper" , "Straitlaced and proper" , "Proper or prissy" .)