For words that have only three letters, there is absolutely no 4th letter. Such as with the word “increase”, there isn't any much more letters afterwards and so needs to be the word "incorporate". The word “addict” is while in the BIP39 wordlist however you would have made use of https://bookmarkingdepot.com/story19075556/how-much-you-need-to-expect-you-ll-pay-for-a-good-valid-bip39-seed-phrase