In the play Macbeth, Ross says "His highness is not well" to indicate that King Duncan is not feeling well. This line is spoken in Act II, Scene 3, after Macbeth has murdered King Duncan and Ross has discovered his body.
Ross uses the term "his highness" to refer to the king because this was a common way to address royalty in Shakespeare's time. By saying "his highness is not well," Ross is trying to convey that something is seriously wrong with the king's health, without explicitly stating that he has been murdered.
This line also serves to heighten the tension and drama of the scene, as Ross's words hint at the violence that has occurred offstage and foreshadow the chaos that will follow in the wake of Duncan's death.