Something that causes the eyes to open, or that opens the eyes.
Something that provides a sudden insight, or makes something clear that was previously mysterious.
A startling or shocking revelation.
A visit to the slaughterhouse was a real eye-opener to anyone who thought they understood where their food came from.
A strong alcoholic beverage, especially one consumed in the morning.
As soon as I got on the plane I asked the flight attendant for an eye-opener, but all he had to offer was orange juice.
An attractive woman.