Related Clues:

• Beethoven's Opus 20 is one
• Trio plus four
• Trio + four
• Work for seven
• Piece for seven
• A series or group of seven
• Seven for music
• Seven performers
• A group of seven
• Group of seven performers
• A group of seven, say singers
• A set of seven
• Group of seven voices
• In short, one month and the parts of it
• Such a short month, and there's only seven in it