For words that only have three letters, there isn't a 4th letter. For instance with the word “incorporate”, there aren't any a lot more letters afterwards and thus must be the word "increase". The word “addict” is from the BIP39 wordlist however, you would have employed “addi” for “addict”. bip39-phrase.com https://bookmarkity.com/story18884009/new-step-by-step-map-for-bip39-english-words