For words that have only three letters, there isn't a 4th letter. For instance with the word “increase”, there aren't any additional letters afterwards and so need to be the word "add". The word “addict” is inside the BIP39 wordlist however , you might have made use of “addi” for https://sociallweb.com/story4603852/top-guidelines-of-bip39-word-list-pdf