Be litigious (3)
I believe the answer is:
sue
'be litigious' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sue that I've seen before include "Take case against in court" , "Litigious girl" , "The girl to take to court" , "Seek legal redress" , "Take legal action against (someone), girl's name" .)