For words that only have three letters, there isn't any 4th letter. By way of example with the word “include”, there aren't any additional letters afterwards and so must be the word "incorporate". The word “addict” is from the BIP39 wordlist but you might have utilized “addi” for “addict”. In https://7prbookmarks.com/story19634689/detailed-notes-on-copyright-wallet-seed-phrase-out-of-bip39