For words that have only 3 letters, there is not any 4th letter. One example is with the word “include”, there isn't any extra letters afterwards and thus has to be the word "increase". The word “addict” is in the BIP39 wordlist but you might have utilised “addi” for “addict”. https://webnowmedia.com/story4180913/5-simple-techniques-for-bip39-word-list-pdf