For words that have only 3 letters, there is not any 4th letter. By way of example with the word “include”, there aren't any more letters afterwards and therefore should be the word "increase". The word “addict” is from the BIP39 wordlist however you would have used “addi” for “addict”. https://mnobookmarks.com/story18882384/how-much-you-need-to-expect-you-ll-pay-for-a-good-valid-bip39-seed-phrase