For words that only have three letters, there isn't any 4th letter. One example is with the word “insert”, there won't be any much more letters Later on and therefore should be the word "increase". The word “addict” is during the BIP39 wordlist however you would've made use of “addi” https://lingeriebookmark.com/story8618673/facts-about-bip39-seed-phrase-github-revealed