eye-opener

Short definition from Wiktionary

Noun

1. 1
   Something that causes the eyes to open, or that opens the eyes.
2. 2
   Something that provides a sudden insight, or makes something clear that was previously mysterious.
3. 3
   A startling or shocking revelation.
4. 4
   A strong alcoholic beverage, especially one consumed in the morning.
5. 5
   An attractive woman.
6. 6
   Alternative form of eye-opener.