Crossword Genius

Wonder what a lid could be? (3-6)

Ross

I believe the answer is:

eye-opener

I'm a little stuck... Click here to teach me more about this clue!

'wonder' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for eye-opener that I've seen before include "Startling revelation" , "Fact that brings great surprise, dilating optics" , "Fact that surprises or enlightens in optical way" , "Unexpected revelation" , "Surprising fact - like wake up call" .)

I've seen this clue in The Sunday Times.
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