For words that only have three letters, there isn't a 4th letter. By way of example with the word “incorporate”, there aren't any a lot more letters afterwards and therefore have to be the word "add". The word “addict” is in the BIP39 wordlist however you might have employed “addi” https://bookmarkingace.com/story18841587/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool