For words that have only 3 letters, there is absolutely no 4th letter. For example with the word “incorporate”, there isn't any a lot more letters Later on and so have to be the word "add". The word “addict” is during the BIP39 wordlist however , you would've utilized “addi” https://followbookmarks.com/story19079438/little-known-facts-about-bip39-seed-phrase-list