For words that only have 3 letters, there isn't a 4th letter. By way of example with the word “incorporate”, there isn't any more letters afterwards and therefore need to be the word "insert". The word “addict” is from the BIP39 wordlist however you would've utilised “addi” for “addict”. bip39-phrase.com https://sparxsocial.com/story9118656/little-known-facts-about-bip39-words