For words that have only 3 letters, there's no 4th letter. As an example with the word “increase”, there aren't any far more letters afterwards and thus should be the word "add". The word “addict” is within the BIP39 wordlist but you might have applied “addi” for “addict”. You might https://bookmarkize.com/story19050747/little-known-facts-about-bip39-seed-phrase-list