The word has a somewhat weak force these days. We associate it with an irritation that things are not turning out as we want - if mail doesn't arrive or our bus is delayed. In Shakespeare's time, it had a much stronger meaning. We sense it when Talbot describes his soldier son as performing "Rough deeds of rage and stern impatience" (Henry VI Part 1, IV.vii. 8).
Here, it means "anger, rage". This meaning is crucial if we are to avoid the word seeming incongruous at the end of Coriolanus (V.vi.146). After Aufidius helps to murder Coriolanus, a lord says, "His own impatienceTakes from Aufidius a great part of blame". Only the sense of "fury" works here; mild irritation is hardly reason enough to launch an assassination. As the Earl of Pembroke, angry to the point of rebellion against the King, says:
"impatience hath his privilege" (King John, IV.iii.32).
David Crystal is author, with Ben Crystal, of Shakespeare's Words, published by Penguin