For words that only have three letters, there's no 4th letter. By way of example with the word “incorporate”, there aren't any extra letters afterwards and so have to be the word "include". The word “addict” is inside the BIP39 wordlist however , you might have made use of “addi” https://loanbookmark.com/story18932150/facts-about-bip39-seed-phrase-github-revealed