—adj. 1. causing or tending to cause death; fatal; lethal: a deadly poison. 2. aiming to kill or destroy; implacable: a deadly enemy. 3. like death: a deadly pallor. 4. excruciatingly boring: The dinner party was absolutely deadly. 5. excessive; inordinate: deadly haste. 6. extremely accurate: Annie Oakley was a deadly shot.
—adv. 1. in a manner resembling or suggesting death: deadly pale. 2. excessively; completely: deadly dull.