For words that only have three letters, there's no 4th letter. For example with the word “increase”, there won't be any a lot more letters afterwards and so need to be the word "include". The word “addict” is within the BIP39 wordlist however, you might have utilised “addi” for “addict”. https://hotbookmarkings.com/story18847834/details-fiction-and-bip39