For words that only have 3 letters, there isn't a 4th letter. Such as with the word “add”, there are no a lot more letters afterwards and therefore must be the word "include". The word “addict” is within the BIP39 wordlist but you would've employed “addi” for “addict”. BIP39 and https://ok-social.com/story4340740/top-guidelines-of-bip39-word-list-pdf