For words that have only three letters, there is absolutely no 4th letter. For example with the word “add”, there isn't any much more letters afterwards and thus should be the word "incorporate". The word “addict” is while in the BIP39 wordlist however, you would've applied “addi” for “addict”. bip39-phrase.com https://peakbookmarks.com/story19069462/bip39-phrase-generator-can-be-fun-for-anyone