For words that have only three letters, there is absolutely no 4th letter. One example is with the word “add”, there won't be any more letters afterwards and thus must be the word "incorporate". The word “addict” is during the BIP39 wordlist however you might have utilised “addi” for “addict”. https://health-lists.com/story19666402/little-known-facts-about-bip39-seed-phrase-list