1. 1. A thin line or narrow beam of light or other radiant energy.
   2. A graphic or other representation of such a line.
2. Radiance; light.
3. A small amount; a trace: not a ray of hope left.
4. Mathematics. A straight line extending from a point. Also called half-line.
5. A structure or part having the form of a straight line extending from a point.
6. Any of the bright streaks that are seen radiating from some craters on the moon.
7. Botany.
   1. A ray flower or the corolla of a ray flower.
   2. A branch of an umbel.
8. Zoology.
   1. One of the bony spines supporting the membrane of a fish's fin.
   2. One of the arms of a starfish or other radiate animal.
9. rays Slang. Sunshine: Let's go to the beach and catch some rays.

1. To send out as rays; emit.
2. To supply with rays or radiating lines.
3. To cast rays on; irradiate.

[Middle English, from Old French rai, from Latin radius.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.