They have a balanced relationship with roundabouts (6)
I believe the answer is:
swings
'roundabouts' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Maybe they are linked in a way I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for swings that I've seen before include "Moves in a curve" , "What you might lose on them, you could gain on the roundabouts" , "Moves back and forth or from side to side while suspended" , "What you lose on these, you hopefully gain on the roundabouts" , "What you lose on these, you'll gain on the roundabouts" .)