For words that only have 3 letters, there is no 4th letter. One example is with the word “insert”, there won't be any much more letters afterwards and so need to be the word "add". The word “addict” is in the BIP39 wordlist however , you would've utilized “addi” for https://tornadosocial.com/story4560664/top-latest-five-bip39-words-urban-news