Line up for a thrilling walk (9)
I believe the answer is:
tightrope
'line up' is the definition.
(line that's up in the air)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for tightrope that I've seen before include "Difficult thing to walk on" , "Cable on which acrobatics are performed" , "Acrobat's walkway" , "Entertaining line" , "Acrobat's wire" .)