For words that only have 3 letters, there's no 4th letter. Such as with the word “increase”, there aren't any much more letters afterwards and so need to be the word "add". The word “addict” is within the BIP39 wordlist however , you would have made use of “addi” for https://myfirstbookmark.com/story19051436/fascination-about-bip39-english-words