For words that have only 3 letters, there isn't a 4th letter. One example is with the word “incorporate”, there isn't any far more letters afterwards and so has to be the word "increase". The word “addict” is during the BIP39 wordlist however you would've utilised “addi” for “addict”. On http://andersonsaeu988.iamarrows.com/from-mnemonics-to-safety-and-security-recognizing-bip39-passphrases-and-their-significance-in-copyright