Is taken aback in cavalier fashion? (5)
I believe the answer is:
rides
'is' is the definition.
The definition and answer can be both to do with fundamental existence as well as being verbs in their -s form.
Perhaps you can see an association between them that I can't see?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for rides that I've seen before include "Theme park features" , "is carried" , "Travels on an animal" , "Goes on a horse" , "Comes through" .)