Zander,
The adjective 'habitable' is derived from the verb "to habit" meaning "to live in." It is an archaic or rarely used verb, although I have come across this word in modern prose several times.
-18 May 2012 – Many houses were inundated with water and many of them lost their belongings as they habited the low lying banks of the river.
The logical opposite of habitable "inhabitable" was once used with its negative meaning. It is now considered obsolete, meaning not only that it is archaic, but that its use would be misinterpreted.
-1674 People towards the North, living in a climate almost inhabitable.
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The modern adjective 'inhabitable' is derived from the verb "to inhabit", which means "to live in."
-The house is in such poor condition that it is barely inhabitable.
The opposite of inhabitable is "uninhabitable."
-Flooding made the building uninhabitable.
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The original usage of habitable/inhabitable agrees with the Longman definition, but modern usage has expanded the meaning to include animals.
-if a place is inhabitable, people and animals can live there...Macmillan English Dictionary for Advanced Learners
-Several hundred species of birds inhabit the island...Merriam Webster Advanced Learners Dictionary
-habitable ....fit to inhabit...Collins Thesaurus of the English Language
-Winter can be tough on birds that don't migrate south to find more habitable conditions.