Shelter has a new occupant (6)
I believe the answer is:
tenant
'occupant' is the definition.
(tenant is a kind of occupant)
'shelter has a new' is the wordplay.
'shelter' becomes 'tent' (tent is a kind of shelter).
'has' means one lot of letters goes inside another.
'a new' becomes 'an' (I've seen this in other clues).
'tent' enclosing 'an' is 'TENANT'.
(Other definitions for tenant that I've seen before include "Anne Bronte's novel 'The ...... of Wildfell Hall'" , "One renting property" , "Leaseholder" , "One who pays the landlord" , "Lessee" .)