Related Clues:

• Morse __
• See 21 Across
• Word with bar or zip
• Nothing, on scoreboards
• Protect from spies, in a way
• Celsius equivalent of 32 degrees Fahrenheit
• Not a thing
• __ of ethics
• Building contractor's study
• Problem for a cracker?
• Morse made one
• Friend of Beetle Bailey
• Create, as a cryptogram
• None
• Complete drip