Crossword Genius

Harry’s track an old song (5,3)

Ross

I believe the answer is:

hound dog

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'an old song' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'harry's track' is the wordplay.
'harry' becomes 'hound' (both can mean to harass).
'track' becomes 'dog' (synonyms).
'hound'+'dog'='HOUND DOG'

Can you help me to learn more?

(Other definitions for hound dog that I've seen before include "Elvis song" , "Writing desk" .)

I've seen this clue in The Sun.
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