Be an unwanted visitor from abroad (6)
I believe the answer is:
invade
'be' is the definition.
(I know that invade is a more specific form of inhabit)
'from abroad' is the wordplay.
'from' becomes 'in' (I've seen this in other clues).
'abroad' becomes 'vade' (I can't justify this - if you can you should give a lot more credence to this answer).
'in'+'vade'='INVADE'
'an unwanted visitor' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for invade that I've seen before include "Enter intrusively" , "Encroach upon" , "Enter illegally" , "Overrun" , "Enter a country by force with an army" .)