I've chosen "whisper" as a medium difficulty word. It's 7 letters long, contains only standard English letters, and is a real English word (not a proper noun or acronym). It's moderately challenging because it contains the less common letter 'w' and has the consonant combination 'wh' at the beginning. The word is recognizable but not among the most frequently used words in everyday conversation, making it a fair challenge for the opponent without being obscure.