For words that have only 3 letters, there isn't a 4th letter. As an example with the word “increase”, there won't be any additional letters Later on and therefore needs to be the word "insert". The word “addict” is inside the BIP39 wordlist however, you would've made use of “addi” https://bookmarksbay.com/story18878287/top-latest-five-bip39-words-urban-news