不宣而戰 [－－－战]

Jyutping bat1 syun1 ji4 zin3
Pinyin bù xuān ér zhàn

Definitions (CC-CEDICT)
  1. open hostilities without declaring war
  2. start an undeclared war
Definitions (Wiktionary)
  1. phrase, idiomatic
    to open hostilities without declaring war; to start an undeclared war
Definitions (Kaifangcidian)
  1. （沒有對應漢語詞彙）