For words that have only three letters, there's no 4th letter. For instance with the word “insert”, there won't be any much more letters Later on and so should be the word "incorporate". The word “addict” is in the BIP39 wordlist however, you would've made use of “addi” for “addict”. https://bookmarkingace.com/story18815482/bip39-phrase-generator-can-be-fun-for-anyone