For words that have only 3 letters, there is not any 4th letter. As an example with the word “increase”, there aren't any more letters afterwards and so have to be the word "incorporate". The word “addict” is in the BIP39 wordlist however , you might have used “addi” for https://bookmarks4seo.com/story18818651/bip39-seed-phrase-mnemonics-generator-an-overview