For words that have only 3 letters, there's no 4th letter. For example with the word “increase”, there aren't any a lot more letters Later on and thus must be the word "add". The word “addict” is from the BIP39 wordlist however you might have made use of “addi” for https://bookmarkize.com/story18854570/the-definitive-guide-to-bip39-seed-phrase