Specify page concerning writer (9)
I believe the answer is:
prescribe
'specify' is the definition.
(thesaurus)
'page concerning writer' is the wordplay.
'page' becomes 'p'.
'concerning' becomes 're'.
'writer' becomes 'scribe' (scribe is a kind of writer).
'p'+'re'+'scribe'='PRESCRIBE'
(Other definitions for prescribe that I've seen before include "Recommend as beneficial" , "Advise use of (medicine)" , "Order use of (medicine or other treatment)" , "Lay" , "as doctor may order" .)