龜鏡 [龟镜]

Jyutping gwai1 geng3
Pinyin guī jìng

Definitions (Wiktionary)
  1. noun, figuratively
    warning; self-criticism; object lesson
    (syn.) 龜鑒, 龟鉴
Definitions (Kaifangcidian)
  1. （沒有對應漢語詞彙）