tidemark

• POS: Noun
• HYPHEN: tide=mark

CIDE DICTIONARY

tidemark, n. 

•  a mark on a shore line indicating the normal level of the water at high tide, caused by the action of the flowing water; sometimes also used for the mark left at the point of the normal low tide; -- called also high water mark.  [PJC]
•  the maximum level which some activity has reached and from which it has declined; -- called also high water mark.  [PJC]

OXFORD DICTIONARY

tidemark, n.
1 a mark made by the tide at high water.
2 esp. Brit. a a mark left round a bath at the level of the water in it. b a line on a person's body marking the extent to which it has been washed.