Secret papers suppressed by hospital study (6)
I believe the answer is:
hidden
'secret' is the definition.
(thesaurus)
'papers suppressed by hospital study' is the wordplay.
'papers' becomes 'id' (identification papers).
'suppressed by' says to put letters next to each other.
'hospital' becomes 'h'.
'study' becomes 'den' (I've seen this before).
'id' after 'h' is 'hid'.
'hid'+'den'='HIDDEN'
(Other definitions for hidden that I've seen before include "Obscure" , "behind closed doors" , "Abstruse" , "Concealed, kept secret" , "Covert, obscured" .)