go under

Verb

go under (third-person singular simple present goes under, present participle going under, simple past went under, past participle gone under)

1. To descend into a body of water; to founder.
   • The boat was too heavy and went under.
2. (idiomatic) To collapse or fail, e.g. by going bankrupt.
   • In the crisis, the company was forced to reduce its costs in order to avoid going under.
3. (idiomatic) To die.
   • If we don't get him to a doctor, he'll go under for sure.
   • Good for a fortnight, am I? The doctor told you? He lied.
     I shall go under by morning, and—— Put that nurse outside.1896, Rudyard Kipling, The Mary Gloster
4. (idiomatic) To be named; to call oneself.
   • He goes under the name of Mr X to remain anonymous.
5. To enter a trance, state of hypnosis, etc.
   • "But I went under nicely and I am glad there were some fine materializations."1925 July – 1926 May, A[rthur] Conan Doyle, “(please specify the chapter number)”, in The Land of Mist (eBook no. 0601351h.html), Australia: Project Gutenberg Australia, published April 2019
6. (Australia, slang) To be imprisoned.