For words that only have three letters, there isn't any 4th letter. For instance with the word “increase”, there aren't any additional letters afterwards and thus must be the word "incorporate". The word “addict” is inside the BIP39 wordlist but you might have made use of “addi” for “addict”. BIP39 https://bookmarkfly.com/story18827188/little-known-facts-about-bip39-words