For words that only have three letters, there's no 4th letter. For example with the word “incorporate”, there are no additional letters afterwards and thus has to be the word "incorporate". The word “addict” is inside the BIP39 wordlist however, you would have utilised “addi” for “addict”. A seed phrase, https://thebookmarkid.com/story18915053/top-guidelines-of-bip39-word-list-pdf