For words that only have 3 letters, there isn't a 4th letter. Such as with the word “incorporate”, there isn't any additional letters afterwards and thus has to be the word "incorporate". The word “addict” is from the BIP39 wordlist however , you might have employed “addi” for “addict”. A https://doctorbookmark.com/story18878422/not-known-facts-about-bip39-english-words