ㄓㄣˋㄓㄣˋㄧㄡˇˊzhènzhèn‑yǒucí

振振有词
  1. 認為自己理由充分振振有辭」。 振振有詞自己辯解」。

to speak forcefully and with justice (idiom)​; to argue with the courage of one's convictions