I've chosen "enigma" as a medium-difficulty word. At 6 letters, it falls within the required length. It contains a mix of common vowels (e, i, a) and less common consonants (n, g, m), creating a balanced challenge. The word means "a mystery or puzzle," which is thematically appropriate for Hangman. It's not an extremely common word in everyday conversation, but it's recognized by most English speakers, making it a good medium-difficulty choice.