For words that only have 3 letters, there is not any 4th letter. For example with the word “add”, there won't be any a lot more letters afterwards and thus should be the word "increase". The word “addict” is during the BIP39 wordlist however, you would've utilised “addi” for “addict”. https://ztndz.com/story22054783/considerations-to-know-about-bip39-seed-phrase-generator