un ‧ ac ‧ cus ‧ tomed /ˌʌnəˈkʌstəmd◂/ BrE AmE adjective formal
1 . unaccustomed to (doing) something not used to something:
a country boy, unaccustomed to city ways
2 . [only before noun] not usual, typical, or familiar:
She was completely exhausted by the unaccustomed heat.
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In everyday English, people usually say that they are not used to something rather than unaccustomed to it:
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She wasn't used to living on her own.