I've selected "rhythm" as a hard difficulty word. It's particularly challenging because it contains no traditional vowels (a, e, i, o, u), with 'y' serving as the only vowel sound. The word is 6 letters long, contains only English letters, and is a legitimate English word referring to a strong, regular pattern of movement or sound. The uncommon letters and unusual letter pattern make it quite difficult to guess, as players often start with common vowels which aren't present.