For words that have only 3 letters, there isn't any 4th letter. For instance with the word “increase”, there aren't any more letters Later on and therefore should be the word "add". The word “addict” is inside the BIP39 wordlist however you would have used “addi” for “addict”. BIP39 and https://socialrus.com/story18295673/a-review-of-bip39-passphrase