For words that only have three letters, there is absolutely no 4th letter. By way of example with the word “incorporate”, there aren't any a lot more letters afterwards and thus needs to be the word "increase". The word “addict” is from the BIP39 wordlist but you might have utilised https://todaybookmarks.com/story19142061/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition