I selected "mystify" as a medium difficulty word for Hangman. At 7 letters, it fits within the length requirements. It contains some less common letters like 'y' (which appears twice) and 'f', making it moderately challenging without being obscure. It's a legitimate English verb meaning "to puzzle or confuse someone," and contains no special characters, spaces, or hyphens. This word should provide a good balance of challenge and fairness for the opponent.