Eve (noun)

1. The day or night before an event or holiday.
2. The evening before a day that is specified or implied.

Origin:

From middle english eue, from old english ēfen, from proto-germanic *aiznaz ("evening"), from proto-indo-european *h₁ey- ("to shine, be bright").

Examples:

1. We"re having a party on New Year"s Eve.
2. The store was closed on Christmas Eve.
3. He proposed to her on the eve of their tenth anniversary.
4. The night before the wedding is often referred to as the eve of the big day.
5. On the eve of the battle, the soldiers were filled with both fear and determination.