[hahy-waw-ter, -wot-er] 
| 1. | a mark showing the highest level reached by a body of water. |
| 2. | the highest point of anything; acme: Her speech was the high-water mark of the conference. |
| high-water mark n.
|
high-water mark
The peak of something, especially an achievement. For example, This composition is the high-water mark of his entire output. This expression alludes to the highest mark left on shore by the tide. [Mid-1800s]