1. a mark left by the tide at its highest or lowest point
Usage: nautical
2. a dirty mark or stain, especially around a bathtub or sink
Usage: British; informal

Examples

• The tidemark on the beach showed where the water had reached during high tide.
• Seaweed and debris collected along the tidemark after the storm.
• She scrubbed the tidemark around the bathtub with bleach.
• The old tidemark on the bathroom wall needed repainting.
• Marine biologists studied the organisms living near the tidemark.
• He noticed a dark tidemark where the floodwater had receded.