For words that have only three letters, there is absolutely no 4th letter. For example with the word “add”, there isn't any far more letters Later on and therefore should be the word "include". The word “addict” is in the BIP39 wordlist however, you would've utilised “addi” for “addict”. Tips https://dirstop.com/story21834747/the-ultimate-guide-to-bip39-seed-phrase-github