Like an old and gory rhyme (5)

I believe the answer is:

hoary

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

'like an old' is the definition.
'hoary' can be an answer for 'old' (I've seen this before). I am not sure about the 'like an' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for hoary that I've seen before include "Ancient and venerable" , "Having grey or white hair" , "White or grey with age" , "Grizzly - ancient" , "Grizzled or frosted" .)

I've seen this clue in the Evening Standard.

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