housemate vs occupier

housemate and occupier both are nouns.

Word	Noun	Adjective	Verb	Adverb
housemate	Yes	No	No	No
occupier	Yes	No	No	No

As nouns, occupier is a hypernym of housemate; that is, occupier is a word with a broader meaning than housemate:

housemate: someone who resides in the same house with you
occupier: someone who lives at a particular place for a prolonged period or who was born there

Other hypernyms of housemate include occupant, resident.

housemate (noun)	occupier (noun)
someone who resides in the same house with you	someone who lives at a particular place for a prolonged period or who was born there
	a member of a military force who is residing in a conquered foreign country