tidemark
Concise Oxford English Dictionary © 2008 Oxford University Press:
tidemark/ˈtʌɪdmɑːk/
▶noun
- 1 a mark left or reached by the sea on a shore at the highest point of a tide.
- 2 Brit. informal a grimy mark left around the inside of a bath or washbasin at the level reached by the water.
'tidemark' also found in these Oxford entries:

