For words that only have three letters, there is not any 4th letter. By way of example with the word “add”, there aren't any a lot more letters Later on and so have to be the word "increase". The word “addict” is from the BIP39 wordlist however, you would've utilised https://doctorbookmark.com/story19000679/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting