I've chosen "rhythm" as a medium-difficulty word. It's 6 letters long and follows all requirements: only contains letters a-z, is a real English word, and has no spaces or special characters. What makes it particularly interesting for Hangman is that it contains no traditional vowels (a,e,i,o,u), using only 'y' as a vowel sound. This creates a nice challenge as players often start with common vowels. It's also a familiar word that most people know, but its unusual letter pattern makes it a perfect medium-difficulty choice for Hangman.