In Hamlet Act 1, Scene 2, Polonius said:
He hath, my lord, wrung from me my slow leave
By laborsome petition, and at last
Upon his will I sealed my hard consent.
What does it mean by slow?
The confusing word here is "leave", because it's used in an old-fashioned sense of "to give permission". As the Cambridge Dictionary has it:
leave noun (PERMISSION)
[ U ] formal
permission or agreement:
He did it without (my) leave.
Did you get leave to do that?
So "wrung my slow leave" means that Laertes (he) has gradually persuaded Polonius to give permission, by repeatedly asking and stating arguments (laboursome petition) in favour of Laertes going to France.