Bip39. Since the 24th is usually a checksum word, a list of 8 legitimate prospect words are calculated using the Python script 24thword.py. For words that have only three letters, there isn't any 4th letter. For example With all the word “add”, there isn't any far more letters Later on https://webtechdirectory.com/listings13114572/bip39-wallet-https-linktr-ee-bip39-not-known-details-about-bip39-online