For words that only have three letters, there's no 4th letter. Such as with the word “include”, there isn't any additional letters afterwards and therefore must be the word "include". The word “addict” is inside the BIP39 wordlist however , you would have used “addi” for “addict”. BIP39 and 44, https://tetrabookmarks.com/story19018877/new-step-by-step-map-for-bip39-english-words