For words that have only three letters, there is absolutely no 4th letter. As an example with the word “increase”, there isn't any a lot more letters afterwards and thus should be the word "increase". The word “addict” is while in the BIP39 wordlist however, you would have applied “addi” http://josueaqpi312.huicopper.com/from-words-to-riches-just-how-to-successfully-make-use-of-bip39-passphrases-for-your-copyright-budgets