unaccustomed

1. Not used to an event or thing, not accustomed.
   • 1749, Henry Fielding, The History of Tom Jones, a Foundling. In Six Volumes, volume (please specify ), London: Printed by A[ndrew] Millar, […], OCLC 928184292 ↗:

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     I again conveyed his key into his pocket, and counterfeiting sleep—though I never once closed my eyes, lay in bed till after he arose and went to prayers—an exercise to which I had long been unaccustomed.

   He is unaccustomed to the cold.

1. Simple past tense and past participle of unaccustom