Related Clues:

• Be honest (with)
• Line on which y = 0
• Video game stage
• Place for Cartesian coordinates
• Graph of y = 0
• Make flat
• Either way, it's flat
• Raze
• On an even keel
• It can follow the last word of 20-, 27-, 47- and 53-across
• Tool-box item
• Flat, as a field
• Parking-garage division
• Graph basis
• At the same height