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Definition of Unheard-of
1. Adjective. Previously unknown. "Developments on an unheard-of scale" 
Similar to: Unknown
Definition of Unheard-of
1. Adjective. Previously unknown; unprecedented ¹
¹ Source: wiktionary.com
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1. Adjective. Previously unknown. "Developments on an unheard-of scale" 
1. Adjective. Previously unknown; unprecedented ¹
¹ Source: wiktionary.com