羽書 [－书]

Jyutping jyu5 syu1
Pinyin yǔ shū

Definitions (Wiktionary)
  1. noun, literary, poetic
    urgent letter; message of emergency (literally, "feathered letter", a letter that flies like a bird)
Definitions (Kaifangcidian)
  1. （沒有對應漢語詞彙）