For words that have only 3 letters, there isn't any 4th letter. Such as with the word “incorporate”, there are no additional letters afterwards and so have to be the word "include". The word “addict” is within the BIP39 wordlist however , you would have applied “addi” for “addict”. BIP39 https://bookmarkerz.com/story18808443/a-review-of-bip39