For words that only have 3 letters, there is absolutely no 4th letter. By way of example with the word “incorporate”, there isn't any additional letters Later on and therefore has to be the word "increase". The word “addict” is within the BIP39 wordlist but you would've used “addi” for https://opensocialfactory.com/story19640510/examine-this-report-on-bip39-mnemonic-phrase-tool