kè gǔ míng xīn
lit. carved in bones and engraved in the heart (idiom)
fig. etched in one's memory
unforgettable
kè gǔ
ingrained
entrenched
deep-rooted
míng xīn kè gǔ
engraved in one's heart and carved in one's bones (idiom); to remember a benefactor as long as one lives
undying gratitude
kè gǔ xiāng sī
deep-seated lovesickness (idiom)