I've selected "quizzical" as a hard difficulty word for Hangman. It's 9 letters long, contains only English letters, and is a real English word (not a proper noun or acronym). It has uncommon letters like 'q' and 'z' which appear twice, making it challenging to guess. The word follows a somewhat unusual spelling pattern, and while it's a legitimate English adjective meaning "suggesting puzzlement," it's not used in everyday conversation, adding to the difficulty.