For words that have only three letters, there's no 4th letter. For example with the word “add”, there isn't any a lot more letters afterwards and so has to be the word "include". The word “addict” is during the BIP39 wordlist however , you would've utilised “addi” for “addict”. You https://bookmark-template.com/story22076145/5-essential-elements-for-bip39-explained