For words that only have 3 letters, there's no 4th letter. By way of example with the word “incorporate”, there aren't any much more letters Later on and therefore must be the word "insert". The word “addict” is inside the BIP39 wordlist however, you would have made use of “addi” https://45listing.com/story20703637/the-definitive-guide-to-bip39-seed-phrase