For words that only have 3 letters, there isn't any 4th letter. As an example with the word “add”, there are no far more letters afterwards and therefore should be the word "increase". The word “addict” is from the BIP39 wordlist however you would've employed “addi” for “addict”. How to https://totalbookmarking.com/story18842116/bip39-seed-phrase-mnemonics-generator-an-overview