What may cover Pisces or Libra (6)
I believe the answer is:
scales
'libra' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for scales that I've seen before include "Set of balances" , "Removes plaque" , "Climbs the weight measuring device" , "Flakes of fish skin" , "Climbs - balances" .)