For words that only have three letters, there isn't a 4th letter. By way of example with the word “include”, there aren't any extra letters afterwards and so has to be the word "include". The word “addict” is during the BIP39 wordlist however you would've used “addi” for “addict”. Artwork https://bookmarkinglog.com/story18800868/considerations-to-know-about-bip39-word-list-pdf