For words that have only three letters, there is no 4th letter. For instance with the word “add”, there aren't any additional letters Later on and so have to be the word "include". The word “addict” is from the BIP39 wordlist however , you would've utilised “addi” for “addict”. - https://kingslists.com/story20003417/top-latest-five-bip39-seed-phrase-mnemonics-generator-urban-news