Crossword Genius

But there is a Cowardly one (4)

Ross

I believe the answer is:

lion

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

'one' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for lion that I've seen before include "Cat, the king of the beasts" , "King of the forest" , "Cowardly visitor in Oz" , "The -, the Witch and the Wardrobe" , "Touring rugby player" .)

I've seen this clue in the Evening Standard.
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