For words that have only three letters, there isn't a 4th letter. By way of example with the word “include”, there won't be any far more letters afterwards and thus must be the word "add". The word “addict” is from the BIP39 wordlist but you would've employed “addi” for “addict”. https://natural-bookmark.com/story19437013/little-known-facts-about-bip39-words