For words that have only three letters, there is not any 4th letter. By way of example with the word “include”, there aren't any much more letters Later on and so have to be the word "add". The word “addict” is from the BIP39 wordlist however you would've employed “addi” https://bookmarkahref.com/story18916145/not-known-facts-about-bip39-english-words