grateful; indebted
忝いお言葉、恐悦至極。
Your gracious words are truly overwhelming, my lord.
あの時のご恩は、まことに忝かった。
I was truly indebted for your kindness at that time.
このご厚情、忝くて、感謝の言葉も出ませぬ。
I am so overwhelmed by this kindness that I cannot find the words to express my gratitude.