For words that have only 3 letters, there isn't any 4th letter. As an example with the word “add”, there won't be any a lot more letters afterwards and therefore has to be the word "increase". The word “addict” is from the BIP39 wordlist however, you would have used “addi” https://bookmarkfame.com/story18787614/examine-this-report-on-bip39-mnemonic-phrase-tool