For words that have only three letters, there isn't a 4th letter. For example with the word “increase”, there aren't any extra letters afterwards and therefore has to be the word "increase". The word “addict” is within the BIP39 wordlist however you might have applied “addi” for “addict”. By subsequent https://highkeysocial.com/story4296765/new-step-by-step-map-for-bip39-english-words