For words that only have three letters, there is not any 4th letter. As an example with the word “add”, there isn't any a lot more letters afterwards and thus needs to be the word "insert". The word “addict” is during the BIP39 wordlist but you would've employed “addi” for https://zanybookmarks.com/story19075594/new-step-by-step-map-for-bip39-english-words