For words that have only three letters, there's no 4th letter. As an example with the word “include”, there are no far more letters afterwards and so need to be the word "add". The word “addict” is in the BIP39 wordlist however you would have made use of “addi” for https://bookmarking1.com/story19019569/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting