Protect, maintain (8)
I believe the answer is:
preserve
I believe this is a double definition.
'protect' is the first definition.
(preserving is a kind of protecting)
'maintain' is the second definition.
(I know that maintain is a more specific form of enter)
(Other definitions for preserve that I've seen before include "Guard" , "Protect; jam" , "Keep alive, maintain" , "Keep alive; jam" , "Particular interest" .)