For words that have only 3 letters, there is absolutely no 4th letter. For example with the word “include”, there are no far more letters afterwards and so should be the word "include". The word “addict” is within the BIP39 wordlist however you would've made use of “addi” for “addict”. https://bookmarklinking.com/story5605550/detailed-notes-on-copyright-wallet-seed-phrase-out-of-bip39