Surprised, taken aback (8)
I believe the answer is:
startled
I believe this clue is a double definition.
'surprised' is the first definition.
(similar in meaning)
'taken aback' is the second definition.
(startling is a kind of taking aback)
(Other definitions for startled that I've seen before include "Taken by surprise" , "Suddenly alarmed" , "Shocked, alarmed" , "Scared" , "Surprised with fright" .)