For words that have only three letters, there is absolutely no 4th letter. For example with the word “incorporate”, there won't be any much more letters Later on and so has to be the word "incorporate". The word “addict” is in the BIP39 wordlist but you might have utilised “addi” https://indexedbookmarks.com/story18884014/top-latest-five-bip39-words-urban-news