It will accommodate study on one US state just the same (9)
I believe the answer is:
identical
'just the same' is the definition.
(I've seen this before)
'it will accommodate study on one us state' is the wordplay.
'will accommodate' is an insertion indicator (inserted letters are accommodated).
'study' becomes 'den' (den can mean an office or study).
'on' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'us state' becomes 'Cal' (abbreviation for California).
'it' enclosing 'den' is 'ident'.
'ident'+'i'+'cal'='IDENTICAL'
(Other definitions for identical that I've seen before include "showing no change" , "as B and B" , "not distinguished" , "Like two peas in a pod" , "Matching" .)