闻所未闻
wén​suǒ​wèi​wén

unheard-of

  1. 闻 聞 wén adjectiveverb
    to hear
    (literary) to hear; to catch the sound of something
  2. 所 suǒ particle
    [relative]
    Used before a verb to form a noun-like phrase representing the object of the action, meaning "that which" or "what".
  3. 未 wèi adverb
    not yet
    (bound form) not yet; have not; did not; shows that something has not happened or is not yet complete
  4. 闻 聞 wén adjectiveverb
    to hear
    (literary) to hear; to catch the sound of something