The most common and most likely answer to this crossword clue is the 10 letter word EYE-OPENER
I've seen this crossword clue in The Times
E
Y
E
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O
P
E
N
E
R
More clues leading to the result EYE-OPENER
- Something illuminating lid?
- I caught top batsman. Such a shock!
- Watch next to key, a surprising sight
- Speaker’s first person by one leading strikers – notable revelation?
- Perhaps Magritte, creator of unsettling images, the old revolutionary, produces revelation
- Watch first man to take over – it’s a surprise
- One peer happy to take unknown drug for revelatory experience
- Watch Frank about to turn up something revealing
- Watch bat in wonder?
- Look at first batsman — it’s revealing
Buddy explains!

The straight part
We know that "Something illuminating" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case something illuminating = eye-opener.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EYE-OPENER mean?
EYE-OPENER noun- 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 strong alcoholic beverage, especially one consumed in the morning.
- An attractive woman.