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' (canvas shelter).
'has' means one lot of letters goes inside another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'a'+'n'='an'
'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" .)