For words that only have 3 letters, there isn't a 4th letter. As an example with the word “add”, there are no a lot more letters afterwards and thus need to be the word "increase". The word “addict” is while in the BIP39 wordlist however you might have utilised “addi” https://www.animenewsnetwork.com/bbs/phpBB2/profile.php?mode=viewprofile&u=1025088