For words that only have 3 letters, there is not any 4th letter. Such as with the word “add”, there isn't any a lot more letters Later on and therefore has to be the word "add". The word “addict” is during the BIP39 wordlist however you would have made use https://7bookmarks.com/story18866480/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting