For words that have only 3 letters, there is absolutely no 4th letter. One example is with the word “increase”, there won't be any extra letters Later on and so need to be the word "insert". The word “addict” is from the BIP39 wordlist however, you would have made use http://zanevnex175.lowescouponn.com/unlocking-the-power-of-bip39-an-extensive-consider-word-lists-and-secure-pocketbooks