heartfelt thanks; deep gratitude
A formal, somewhat literary expression of profound gratitude, often used in written acknowledgments or speeches.
ご支援に厚礼を申し上げます。
I express my heartfelt thanks for your support.
厚礼の言葉もございません。
I have no words to express my deep gratitude.
Composed of 厚 (thick, deep, profound) and 礼 (thanks, etiquette). The exact historical derivation is uncertain, but the kanji combination naturally conveys the meaning of deep gratitude.