Other forms: rays
A ray is a narrow line of light travelling out from something bright. Think of the rays coming through a gap in the curtains with the dust turning in them, or the ones that break through cloud after rain.
In the plural, rays are what the sun sends down on you: the sun's rays, UV rays, put sunscreen on before you catch some rays. Science uses the word for streams of energy that are not light at all — X-rays at the hospital, gamma rays from space. Maths has its own ray: a line that starts at one point and runs on for ever in one direction. There is a fish called a ray, flat as a plate, gliding along the sea floor with a whip of a tail. And the figurative one everyone knows: a ray of hope, the single bright thing in a dark week.
1nounrayA narrow line of light travelling out from something bright.
“A ray of sunlight fell across the kitchen floor.”
2nounstreamA stream of energy or particles sent out from something.
“The cream protects your skin from the sun's rays.”
3nounsmallA small sign of something good in a difficult situation.
“The letter was the first ray of hope they had had in months.”
4noungeometryIn geometry, a line that begins at one point and continues for ever in one direction.
“Draw a ray from the centre of the circle through point B.”
5nounflatA flat sea fish with wide wing-like fins and a long thin tail.
“A ray slid over the sand and disappeared.”
Too few real examples of this word to estimate which sense is commonest.
ray is a line of light.
Ray came into English from Old French rai, from Latin radius, which meant a staff, a stake, or the spoke of a wheel. Look at a wheel and you can see why: the spokes shoot out from the centre exactly the way light does. The same Latin word came into English a second time, unchanged, as radius.
Latin
radius — staff, stake, spoke
Old French
rai
English, today
ray
Via Middle English -, borrowed from Old French rai, from Latin radius (“staff, stake, spoke”). a doublet of radius.
Etymology from Wiktionary, CC BY-SA