I've selected "quartz" as a medium difficulty word for Hangman. It's 6 letters long (between the required 4-10 range) and contains only standard English letters. What makes it moderately challenging is that it includes the uncommon letters 'q' and 'z', and has only one vowel ('a'). It's a real English word (a mineral) that most people would recognize, but not use in everyday conversation. It has no spaces, hyphens, or special characters, and it's not a proper noun or acronym.