Related Clues:

• D or F
• Importance
• Do, e.g.
• It's passed in class
• Folding money
• Post-it, e.g.
• Brief communication
• Post-it message
• Do, for example
• Memorandum
• Memory jogger
• A security
• Do, re or mi
• Semiquaver, e.g.
• Do on a scale