For words that only have 3 letters, there is no 4th letter. For instance with the word “include”, there isn't any more letters afterwards and therefore must be the word "incorporate". The word “addict” is during the BIP39 wordlist however you would have applied “addi” for “addict”. Mnemonic words examples https://bookmarkinginfo.com/story18875558/considerations-to-know-about-bip39-word-list-pdf