Be constantly anxious (4)
I believe the answer is:
fret
'be constantly anxious' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for fret that I've seen before include "Sort of saw work" , "Worry unnecessarily" , "ridge > that obscures sea view" , "Mist coming in from the sea" , "Worry - decoration - part of guitar" .)