English

Noun

first water ‎(uncountable)

1. The highest quality of gemstones, especially of diamonds and pearls.
   • 1880, Cornwall, HB, “Gems and Precious Stones”, in Patterson, WM, editor, The Growing world; or, Progress of civilization, and the wonders of nature, science, literature and art, interspersed with a useful and entertaining collection of miscellany, page 20:

     To be the first water a diamond must be absolutely colorless, very lustrous, and perfectly free from flaws.

2. (by extension) Of the highest rank or quality.

Derived terms

• of the first water