Permit is required to enter Virginia (4)
I believe the answer is:
visa
'permit' is the definition.
(I've seen this before)
'is required to enter virginia' is the wordplay.
'required to enter' means one lot of letters goes inside another.
'virginia' becomes 'va' (US state abbreviation).
'is' going into 'va' is 'VISA'.
(Other definitions for visa that I've seen before include "Passport stamp or well-known credit card" , "travel authority" , "It allows the bearer to enter the country issuing it" , "Addition to passport" , "Stamp affixed to passport as permission to enter country" .)