For words that have only 3 letters, there isn't any 4th letter. As an example with the word “incorporate”, there are no additional letters Later on and therefore must be the word "increase". The word “addict” is while in the BIP39 wordlist but you might have made use of “addi” https://getidealist.com/story20606763/top-latest-five-bip39-words-urban-news