For words that only have 3 letters, there's no 4th letter. As an example with the word “increase”, there won't be any far more letters afterwards and so need to be the word "add". The word “addict” is in the BIP39 wordlist however , you would have utilised “addi” for https://bookmarkshq.com/story20577569/not-known-factual-statements-about-bip39-explained