萬不得已

万不得已
wànbùdéyǐ
only when absolutely essential (idiom); as a last resort

CEDICT

out of absolute necessity; with no other choice; as a last resort

Wiktionary

毫無辦法，不得不如此。

重編國語辭典

毫無辦法，無可奈何，不得不這樣

維基詞典

Entry Composition

1 萬 wàn
  1. ten thousand
  2. a great number
2 不得已 bùdéyǐ
  1. to act against one's will
  2. to have no alternative but to
  3. to have to
  4. to have no choice
  5. must