1. lines on a ship’s hull marking the level to which it sinks in water under different loading conditions
Usage: nautical
2. lines drawn on technical drawings showing where water would meet an object at various levels
Usage: technical
3. marks or stains left by water at different levels on surfaces

Examples

• The ship’s waterlines showed it was carrying a full cargo load.
• Engineers studied the boat’s waterlines to determine its stability.
• The architect drew waterlines on the dock design to show flood levels.
• After the storm, waterlines on the building walls revealed how high the water had risen.
• The marina inspector checked that all boats met safety waterlines requirements.
• Waterlines on the basement walls indicated previous flooding.