For words that have only 3 letters, there isn't any 4th letter. For example with the word “add”, there isn't any additional letters afterwards and so has to be the word "include". The word “addict” is during the BIP39 wordlist however you would have applied “addi” for “addict”. Mnemonic words https://techonpage.com/story4185203/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting