For words that only have three letters, there is not any 4th letter. For example with the word “increase”, there aren't any a lot more letters afterwards and so needs to be the word "incorporate". The word “addict” is within the BIP39 wordlist however , you would've applied “addi” for https://livebookmarking.com/story18898859/bip39-seed-phrase-mnemonics-generator-an-overview