For words that have only three letters, there isn't a 4th letter. By way of example with the word “include”, there aren't any a lot more letters afterwards and thus has to be the word "incorporate". The word “addict” is from the BIP39 wordlist but you might have used “addi” https://thebookmarkage.com/story18783010/the-greatest-guide-to-seed-phrase-bip39