死不瞑目

sǐbùmíngmù
  1. lit. not close one's eyes after dying (idiom)
  2. fig. to die with an unresolved grievance

CEDICT

to die with a grievance or regret

Wiktionary

语出《三国志．卷四六．吴书．孙坚传》：「今不夷汝三族，县示四海，则吾死不瞑目。」指人抱恨而死，心有未甘。《三国演义．第一一回》：「君若捨我而去，我死不瞑目矣！」也作「死不闭目」。

重編國語辭典

指人抱恨而死，内心感到不甘

維基詞典

Entry Composition

1 死 sǐ
  1. to die
  2. impassable
  3. uncrossable
  4. inflexible
  5. rigid
  6. extremely
  7. damned
2 不 bù
  1. no; not so
  2. (bound form) not; un-
3 瞑目 míngmù
  1. to close one's eyes
  2. (fig.) to be contented at the time of one's death (Dying without closing one's eyes would signify having unresolved grievances.)