high-water mark

1. 1.

   a line marking the highest level reached

   Broaderwater line

Questions about high-water mark

What does high-water mark mean?

high-water mark means "a line marking the highest level reached".

Is high-water mark a common word?

high-water mark is banded "Rare" — specialist or archaic — most readers will not have met it. The band comes from how often the word appears in a large corpus of everyday English, not from an editor's impression.