For words that only have 3 letters, there is not any 4th letter. By way of example with the word “include”, there isn't any a lot more letters Later on and therefore must be the word "insert". The word “addict” is during the BIP39 wordlist however, you might have used https://wavesocialmedia.com/story4436311/not-known-factual-statements-about-bip39-explained