For words that have only 3 letters, there is not any 4th letter. Such as with the word “incorporate”, there are no additional letters afterwards and therefore has to be the word "increase". The word “addict” is inside the BIP39 wordlist however , you would have employed “addi” for “addict”. https://hotbookmarkings.com/story18922641/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting