tidemark
🇺🇸
/ˈtaɪdmɑːrk/
🇬🇧
/ˈtaɪdmɑːk/
The highest point reached by a tide on a beach or shoreline.
After the storm, the tidemark on the beach was higher than usual.
A line left by dirty water in a bathtub after it has drained.
I noticed a tidemark around the inside of the bathtub after the kids' bath.