Crossword Genius

It's been quick to jump over the lazy dog (3)

Ross

I believe the answer is:

fox

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

'dog' is the definition.
The definition and answer can be both animals as well as being singular nouns.
Maybe they are linked in a way I don't understand?

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for fox that I've seen before include "Puzzle" , "Nonplus" , "Vulpine creature" , "Deceive; Reynard" , "Hunted animal" .)

I've seen this clue in the Evening Standard.
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