For words that have only 3 letters, there is not any 4th letter. By way of example with the word “include”, there isn't any far more letters Later on and thus need to be the word "include". The word “addict” is in the BIP39 wordlist however, you would've used “addi” https://socialrator.com/story9438019/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition