For words that only have three letters, there is not any 4th letter. As an example with the word “incorporate”, there aren't any much more letters Later on and therefore have to be the word "add". The word “addict” is during the BIP39 wordlist but you might have utilized “addi” https://bookmarkspring.com/story13868819/the-ultimate-guide-to-bip39-seed-phrase-github