忠心耿耿

zhōngxīngěnggěng
loyal and devoted (idiom); faithful and true

CEDICT

loyal and devoted

Wiktionary

形容极为忠诚。《镜花缘．第五七回》：「当日令尊、伯伯为国捐躯，虽大事未成，然忠心耿耿，自能名垂不朽。」也作「耿耿忠心」。

重編國語辭典

忠心诚意，形容极为忠诚

維基詞典

Entry Composition

1 忠心 zhōngxīn
  1. good faith
  2. devotion
  3. loyalty
  4. dedication
2 耿耿 gěnggěng
  1. bright
  2. devoted
  3. having sth on one's mind
  4. troubled