For words that only have 3 letters, there isn't any 4th letter. Such as with the word “incorporate”, there are no more letters Later on and thus needs to be the word "incorporate". The word “addict” is inside the BIP39 wordlist however , you might have made use of “addi” https://wiishlist.com/story19411550/considerations-to-know-about-bip39-word-list-pdf