“go under”是一个不及物动词短语，核心含义围绕“向下/消失”的引申，常见义项及用法如下：
指因财务困难或经营不善而停止存在，强调“彻底崩溃”。
英文解释：to fail or cease operating, especially due to financial problems
例句：
1、 Many small businesses went under during the COVID-19 pandemic.（很多小企业在新冠疫情期间破产了。）
2、 If we don’t cut costs, our restaurant will go under by the end of the year.（如果不削减成本，我们的餐馆年底前会倒闭。）
3、 The startup went under after burning through all its investment.（那家初创公司烧光了所有投资后倒闭了。）
指完全没入水面或液体中。
英文解释：to sink below the surface of water/liquid
例句：
1、 The Titanic hit an iceberg and went under in less than three hours.（泰坦尼克号撞上冰山，不到三小时就沉没了。）
2、 The heavy rain caused the basement to go under—we had to pump out the water.（暴雨导致地下室被淹没，我们得把水抽出去。）
3、 The small boat started leaking and went under before help arrived.（小船开始漏水，救援到达前就沉了。）
指因困难过大而停止努力，强调“精神崩溃”或“放弃抵抗”。
英文解释：to stop trying because something is too difficult
例句：
1、 He refused to go under even when he lost his job and his house.（即使失业又失去房子，他也不肯认输。）
2、 Don’t go under—keep fighting! You’ll get through this.（别放弃，继续坚持！你会挺过去的。）
3、 I almost went under when my mom got sick, but my friends supported me.（妈妈生病时我差点崩溃，但朋友帮了我。）
1、 不及物：后面不能直接跟宾语，若需说明“因什么而失败/沉没”，需用介词短语（如go under due to... / go under because of...）。
✖️ 错误：The company went under the crisis.
✔️ 正确：The company went under due to the crisis.（公司因危机倒闭。）
2、 无被动：本身是不及物动词短语，不能用被动语态（如be gone under 是错误表达）。
3、 比喻扩展：可引申为“希望/计划破灭”，如：
His dream of becoming a singer went under when he failed the audition.（他没通过试镜，当歌手的梦想破灭了。）
go under vs. go down：
“go down”也有“下沉”义，但更侧重“下降”（如价格、温度）或“被接受”（如The joke went down well. 这个笑话很受欢迎）；
“go under”更强调“彻底消失/失败”（如企业倒闭、船完全沉没）。
综上，“go under”的核心是“向下/消失”，根据语境可理解为“破产、沉没、屈服”，是口语和书面语中都很常用的短语。