For words that have only 3 letters, there isn't any 4th letter. One example is with the word “add”, there isn't any additional letters Later on and therefore should be the word "increase". The word “addict” is inside the BIP39 wordlist however , you would've used “addi” for “addict”. You https://prbookmarkingwebsites.com/story21911270/the-greatest-guide-to-seed-phrase-bip39