For words that only have three letters, there isn't any 4th letter. One example is with the word “increase”, there aren't any far more letters afterwards and so have to be the word "include". The word “addict” is in the BIP39 wordlist however, you would've used “addi” for “addict”. bip39-phrase.com https://leftbookmarks.com/story18865394/a-review-of-bip39-phrase-list