One in a tent is the occupant (6)
I believe the answer is:
tenant
'the occupant' is the definition.
(tenant is a kind of occupant)
'one in a tent' is the wordplay.
'one' becomes 'an' (an apple is one apple).
'in' is an insertion indicator.
'an' put inside 'tent' is 'TENANT'.
'is' acts as a link.
(Other definitions for tenant that I've seen before include "He pays rent for lodgings" , "Lodger" , "Person renting property" , "One who pays the landlord" , "Resident" .)