1. The line made on the shore by the tide at its utmost height.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• gigh-water mark,
• bigh-water mark,
• nigh-water mark,
• jigh-water mark,
• uigh-water mark,
• yigh-water mark,
• hugh-water mark,
• hjgh-water mark,
• hkgh-water mark,
• hogh-water mark,
• h9gh-water mark,
• h8gh-water mark,
• hifh-water mark,
• hivh-water mark,
• hibh-water mark,
• hihh-water mark,
• hiyh-water mark,
• hith-water mark,
• higg-water mark,
• higb-water mark

The adjective form of "high-water mark" is "high-water".

The plural form of "high-water mark" is "high-water marks".

The singular form of the word "high-water mark" is "high-water mark". The term does not have a distinct singular form and is used to refer to the highest level or point reached by a body of water during a specific period.