The ankle bone that sits between the lower leg bones and the foot, or in architecture, a small decorative rounded molding.
From Greek astragalos meaning 'knucklebone' or 'ankle bone.' The anatomical term was adopted directly; the architectural term came later by analogy to the bone's shape.
The astragalus is the 'talus' in 'talus slope'—it's the only bone in your foot that has no muscles attached to it, which is why it can roll and rotate so freely.
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