A formal, honorific closing formula used at the end of letters, equivalent to 'Yours respectfully' or 'Sincerely yours'. It is a yojijukugo and belongs to sonkeigo register.
Write 'Tonshu saihai' at the end of the letter.
敬具 is a more common and slightly less formal letter-closing phrase, while 頓首再拝 is more elaborate and respectful.
草々 is an informal closing used in casual letters, in contrast to the very formal 頓首再拝.
A yojijukugo composed of 頓首 (bowing deeply) and 再拝 (bowing again), expressing profound respect. The exact historical derivation is uncertain, but it has been used as a formal letter-closing phrase.