Rest that's essential for tightrope-walker? (7)
I believe the answer is:
balance
'rest' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for balance that I've seen before include "Equilibrium or symmetry" , "Sign" , "Rest" , "Weighing device" , "Weighing apparatus" .)