For words that have only 3 letters, there isn't a 4th letter. By way of example with the word “add”, there won't be any much more letters Later on and thus needs to be the word "incorporate". The word “addict” is in the BIP39 wordlist however you might have employed http://collinmmss433.lucialpiazzale.com/opening-the-power-of-bip39-a-comprehensive-check-out-word-lists-and-secure-pocketbooks