銘心鏤骨 [铭－镂－]

Jyutping ming5 sam1 lau6 gwat1
Pinyin míng xīn lòu gǔ

Definitions (CC-CEDICT)
  1. engraved in one's heart and carved in one's bones (idiom); to remember a benefactor as long as one lives
  2. undying gratitude