Crossword Genius

My knowledge may be understood (3)

Ross

I believe the answer is:

lor

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

'my' is the definition.
(exclamation of surprise)

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

Can you help me to learn more?

(Another definition for lor that I've seen is " crumbs".)

I've seen this clue in The Times.
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