For words that have only 3 letters, there is no 4th letter. By way of example with the word “add”, there are no a lot more letters Later on and so must be the word "incorporate". The word “addict” is inside the BIP39 wordlist however , you might have employed https://210list.com/story19405736/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting