For words that have only 3 letters, there isn't a 4th letter. For example with the word “increase”, there won't be any extra letters afterwards and so have to be the word "incorporate". The word “addict” is from the BIP39 wordlist however you would have used “addi” for “addict”. Tips http://rylanmecp341.wpsuo.com/from-words-to-wide-range-exactly-how-to-efficiently-make-use-of-bip39-passphrases-for-your-copyright-pocketbooks