Related Clues:

• Sum of opposites
• Number of remaining dodo birds
• Receiver, as it were
• Acme's opposite
• Operator's number?
• The lowest point to drain into
• Point opposite the zenith
• The lowest point
• Lowest point, or time of deepest depression.
• Nothing, nil
• Cipher for nothing
• Nought
• The lowest part
• Drain to lowest level
• Drain to lowest point