Bird gives one a shock after dark (8)
I believe the answer is:
nightjar
'bird' is the definition.
(nightjar is a kind of bird)
'one a shock after dark' is the wordplay.
'one a shock' becomes 'jar' (I've seen this before).
'after' says to put letters next to each other.
'dark' becomes 'night' (it's dark at nighttime).
'jar' after 'night' is 'NIGHTJAR'.
'gives' is the link.
(Other definitions for nightjar that I've seen before include "flier" , "Nocturnal bird of swift family" , "Nocturnal bird related to the swift" , "Nocturnal bird with harsh cry" , "Nocturnal insect-eating bird" .)