Rule’s strong but suitable to live in (9)

I believe the answer is:

habitable

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'in' is the definition.
Both the answer and definition are adjectives. Perhaps you can see an association between them that I don't see?

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for habitable that I've seen before include "Fit to live in" , "Suitable for living in" .)

I've seen this clue in The Hindu.

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