unheard-of
adjective uk/ʌnˈhɜːd.ɒv/ us/ʌnˈhɝːd.ɑːv/
令人震惊的;前所未闻的,空前的
surprising or shocking because not known about or previously experienced
It was unheard-of for an unmarried couple to live together. 未婚同居,这在以前是闻所未闻的事。
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