For words that only have 3 letters, there's no 4th letter. Such as with the word “increase”, there won't be any a lot more letters afterwards and thus needs to be the word "increase". The word “addict” is during the BIP39 wordlist but you would have made use of “addi” https://bookmarkfame.com/story18883817/the-definitive-guide-to-bip39-seed-phrase