For words that have only 3 letters, there is absolutely no 4th letter. For example with the word “increase”, there aren't any much more letters afterwards and thus must be the word "incorporate". The word “addict” is within the BIP39 wordlist however, you would have made use of “addi” for https://bookmarkworm.com/story19429459/considerations-to-know-about-bip39-seed-phrase-generator