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One often flat out on road, he would pass hospital, say, coming back (8)

Ross

I believe the answer is:

hedgehog

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'one often flat out on road' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'he would pass hospital say coming back' is the wordplay.
'would' becomes 'd' (as in 'we'd' - 'we would').
'pass' becomes 'go' (synonyms).
'hospital' becomes 'H' (abbreviation for hospital).
'say' becomes 'eg' (both can mean 'for example').
'coming back' says the letters should be written in reverse.
'go'+'h'+'eg'='goheg'
'goheg' written backwards gives 'gehog'.
'he'+'d'+'gehog'='HEDGEHOG'

Can you help me to learn more?

(Other definitions for hedgehog that I've seen before include "one often flat out on road?" , "Spiny insect-eater" , "Prickly garden animal" , "Prickly rodent" , "Woodland animal" .)

I've seen this clue in The Guardian.
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