home r Sophie Curtis ray ra⋅di⋅o [rey-dee-oh] –noun 1. a thin line or narrow beam of light or other radiant energy. 2. radiance; light. 3. a small amount; a trace: not a ray of hope left. 4. Mathematics. a straight line extending from a point. 5. a structure or part having the form of a straight line extending from a point. a b c d e f g h i j k l m n o p q r s t u v w x y z rack rain ray rainbow raze radio read reach record recumbent rabbit red-rev rat