Is there less foul play in one? (8)

I believe the answer is:

friendly

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'one?' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?

I cannot understand how the rest of the clue works.

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(Other definitions for friendly that I've seen before include "Amiable" , "on the same side" , "Amicable and kindly" , "Well-disposed" , "match?" .)

I've seen this clue in the Evening Standard.

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