For words that have only 3 letters, there isn't a 4th letter. As an example with the word “add”, there won't be any a lot more letters afterwards and therefore must be the word "incorporate". The word “addict” is inside the BIP39 wordlist but you might have used “addi” for https://socialmediainuk.com/story20492065/bip39-seed-phrase-mnemonics-generator-an-overview