This scene marks Laertes's exit and return to France, from which he had returned for Claudius's coronation. As he is about to leave, Polonius, noting that Laertes is still there, says,
Yet here, Laertes? Aboard, aboard, for shame!
The wind sits in the shoulder of your sail,
And you are stay'd for.
In this case, "stay'd" is a synonym for "waited." As Laertes has delayed his departure by counseling Ophelia about her relationship with Hamlet, Polonius reminds him to hurry up. At the beginning of the scene, audiences learn that Laertes is already packed and has put his belongings on the ship that will take him to France, so Polonius is simply reminding him that the ship is waiting for him.