Marginally nervous? (4)
I believe the answer is:
edgy
'nervous?' is the definition.
('edgy' can be a synonym of 'nervous')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for edgy that I've seen before include "Red shade" , "Keyed up" , "Jittery" , "Visibly nervous" , "Anxious" .)