The modern senses of safe are very old, dating from the 13th century, and by Shakespeare's time they had developed several other meanings, not all of which are used today. Some of these can be especially misleading. When Macbeth asks the First Murderer "But Banquo's safe?" (Macbeth, III.iv.24), this is not a hopeful enquiry about Banquo's state of health. Here, safe means "sure, certain" - in other words, definitely dead! This sense of being "safely out of the way" can also be heard when Miranda tells Ferdinand that her father "is safe for these three hours" (The Tempest, III.i.21). Similarly misleading is the usage heard when King Henry, talking alone with Aumerle, is warned by York that Aumerle is a traitor. "Villain, I'll make thee safe!" says Henry, turning on Aumerle (Richard II, V.iii.40). Here, the sense required is "harmless, not dangerous".
David Crystal is author, with Ben Crystal, of Shakespeare's Words, published by Penguin