eau

Eau is the French word for water. It is used in science, daily language, and many compound terms. The word derives from Latin aqua and is cognate with the English aqua as well as with Spanish agua and Italian acqua.

In French, eau is a feminine noun. It is pronounced roughly "oh" and often appears in phrases describing different kinds of water, such as eau potable (drinking water) and eau chaude (hot water).

In perfumery, eau appears as a label indicating a lighter fragrance concentration than parfum. Common categories include eau de parfum, eau de toilette, and eau de cologne. Typical aromatic compound ranges are about 15–20% for eau de parfum, 5–15% for eau de toilette, and 2–5% for eau de cologne; exact values vary by brand.

Beyond fragrance, eau is used in other contexts to denote water in titles and branding, especially in French-language materials. The term remains central to discussions of linguistics, chemistry, and consumer products.