For words that have only 3 letters, there is not any 4th letter. By way of example with the word “add”, there won't be any much more letters Later on and therefore have to be the word "include". The word “addict” is from the BIP39 wordlist however, you would've utilised https://social40.com/story4289252/considerations-to-know-about-bip39-seed-phrase-generator