Worry, finding line on neck (4)
I believe the answer is:
fret
'worry' is the definition.
(to fret about something is to worry)
'line on neck' is the wordplay.
I cannot quite see how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found within the answer.
This explanation may well be incorrect...
'finding' is the link.
Can you help me to learn more?
(Other definitions for fret that I've seen before include "Sort of saw work" , "Harry - on the guitar" , "Worry, brood" , "Display anxiety" , "Worry - decoration - part of guitar" .)