For words that have only three letters, there's no 4th letter. One example is with the word “incorporate”, there aren't any much more letters Later on and therefore need to be the word "increase". The word “addict” is while in the BIP39 wordlist however you might have made use of https://bookmarkedblog.com/story19901306/how-much-you-need-to-expect-you-ll-pay-for-a-good-valid-bip39-seed-phrase