Worry a fellow (5)
I believe the answer is:
harry
'worry' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for harry that I've seen before include "See 20" , "Persistently harass" , "Hound" , "Harass; man's name" , "Prince William's younger brother" .)