unheard-of
🇺🇸
/ʌnˈhɜːrd əv/
🇬🇧
/ʌnˈhɜːd əv/
adjective
R
Something that has never been known or done before; extremely rare or unusual.
It was unheard-of for a person to travel to the moon, but now it's a reality.
人が月に旅行することは聞いたことがないが、今は現実です。
translation
聞いたことがない