For words that have only 3 letters, there is no 4th letter. Such as with the word “insert”, there isn't any a lot more letters afterwards and therefore should be the word "include". The word “addict” is within the BIP39 wordlist however, you would've made use of “addi” for “addict”. https://hotbookmarkings.com/story18832942/facts-about-bip39-seed-phrase-word-list-revealed