For words that only have 3 letters, there isn't a 4th letter. As an example with the word “include”, there are no a lot more letters afterwards and therefore must be the word "include". The word “addict” is within the BIP39 wordlist however, you might have utilised “addi” for “addict”. https://bookmarkbells.com/story18956992/the-definitive-guide-to-bip39-seed-phrase