For words that have only 3 letters, there is absolutely no 4th letter. As an example with the word “include”, there isn't any extra letters Later on and therefore needs to be the word "include". The word “addict” is during the BIP39 wordlist however you would have made use of https://www.symbaloo.com/embed/shared/AAAACHlsY-AAA42AhQqHKA==