没齿不忘

hard to forget even after one's teeth fall out (idiom); to remember a benefactor as long as one lives; undying gratitude

lit. etched into one's heart and bones (idiom); fig. etched in one's memory; remembered with gratitude as long as one lives

lit. carved in bones and engraved in the heart (idiom); fig. etched in one's memory

engraved in one's heart and carved in one's bones (idiom); to remember a benefactor as long as one lives; undying gratitude

etched in one's bones and heart (idiom); ever-present memory (esp. resentment)

never to be forgotten