For words that have only three letters, there isn't a 4th letter. For instance with the word “add”, there aren't any a lot more letters Later on and therefore should be the word "incorporate". The word “addict” is inside the BIP39 wordlist however you would've applied “addi” for “addict”. Mnemonic https://tetrabookmarks.com/story19061697/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting