Middle part of the passport possibly covered up (3)
I believe the answer is:
hid
'covered up' is the definition.
(I've seen this in another clue)
'middle part of the passport' is the wordplay.
'middle part of' means to look at the middle letters.
'passport' becomes 'id' (a passport is identification).
The central letter of 'the' is 'h'.
'h'+'id'='HID'
'possibly' acts as a link.
(Other definitions for hid that I've seen before include "Remained out of sight" , "Concealed, kept secret" , "Took cover" , "Stayed out of sight" , "Concealed in orchids" .)