Back on the floor? (6)

I believe the answer is:

supine

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'back on the floor?' is the definition.
Both the definition and answer are adjectives. Maybe you can see a link between them that I don't see?

This is the entire clue.

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(Other definitions for supine that I've seen before include "looking up" , "Prostrate" , "Use pin (anag.)" , "Laid-back" , "Recumbent" .)

I've seen this clue in The Guardian.

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