For words that have only three letters, there isn't a 4th letter. As an example with the word “incorporate”, there are no much more letters Later on and therefore have to be the word "add". The word “addict” is in the BIP39 wordlist however, you would have utilised “addi” for https://webnowmedia.com/story4228294/the-2-minute-rule-for-bip39-all-words