For words that only have three letters, there is absolutely no 4th letter. As an example with the word “include”, there isn't any extra letters Later on and thus has to be the word "insert". The word “addict” is in the BIP39 wordlist but you would have used “addi” for https://socialwebconsult.com/story4214566/bip39-phrase-generator-can-be-fun-for-anyone