For words that have only three letters, there is not any 4th letter. As an example with the word “include”, there isn't any far more letters afterwards and so must be the word "increase". The word “addict” is while in the BIP39 wordlist but you would've applied “addi” for “addict”. https://mysocialguides.com/story4226760/the-definitive-guide-to-bip39-seed-phrase