unheard-of

unheard-of
unˈheard of , unheard-of adjective
something that is unheard of is so unusual that it has not happened or been known before:
    Travel for pleasure was almost unheard of until the 19th century.

unheard-ofBrE /ʌnˈhɜːd əv/ 🔊NAmE /ʌnˈhɜːrd əv/ 🔊 adjectivethat has never been known or done; very unusual 前所未闻的；空前的；很反常的◆He'd dyed his hair, which was almost unheard-of in the 1960s. 他染了头发，这在 20 世纪 60 年代是罕见的事。🔊🔊◆It is almost unheard-of for a new band to be offered such a deal. 一支新乐队得到这样的一份合同，几乎是空前的。🔊🔊