A ray is a beam of light or radiation. Even on cloudy days, you sometimes see a ray of sunlight shine through the clouds.

In physics, a ray is a line or column of light, heat, or electromagnetic radiation (like an x-ray), while in math a ray is a line that passes through a specific point. A marine biologist would define a ray as a big fish that's related to sharks and has a wide, flat body and a long tail. The root of the first two kinds of rays is the Latin word radius, "spoke" or "staff."

Definitions of ray
  1. noun
    a group of nearly parallel lines of electromagnetic radiation
    synonyms: beam, electron beam
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    cathode ray
    a beam of electrons emitted by the cathode of an electrical discharge tube
    particle beam
    a collimated flow of particles (atoms or electrons or molecules)
    ion beam, ionic beam
    a beam of ions moving in the same direction at the same speed
    type of:
    electromagnetic radiation, electromagnetic wave, nonparticulate radiation
    radiation consisting of waves of energy associated with electric and magnetic fields resulting from the acceleration of an electric charge
  2. noun
    a column of light (as from a beacon)
    synonyms: beam, beam of light, irradiation, light beam, ray of light, shaft, shaft of light
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    heat ray
    a ray that produces a thermal effect
    high beam
    the beam of a car's headlights that provides distant illumination
    moon ray, moon-ray, moonbeam
    a ray of moonlight
    sunbeam, sunray
    a ray of sunlight
    laser beam
    a beam of light generated by a laser
    low beam
    the beam of a car's headlights that provides illumination for a short distance
    infrared ray
    a ray of infrared radiation; produces a thermal effect (as from an infrared lamp)
    type of:
    light, visible light, visible radiation
    (physics) electromagnetic radiation that can produce a visual sensation
  3. noun
    (mathematics) a straight line extending from a point
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    type of:
    a straight line segment whose length is magnitude and whose orientation in space is direction
  4. verb
    emit as rays
    “That tower rays a laser beam for miles across the sky”
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    type of:
    emit, give off, give out
    give off, send forth, or discharge; as of light, heat, or radiation, vapor, etc.
  5. verb
    extend or spread outward from a center or focus or inward towards a center
    synonyms: radiate
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    type of:
    extend, go, lead, pass, run
    stretch out over a distance, space, time, or scope; run or extend between two points or beyond a certain point
  6. verb
    expose to radiation
    synonyms: irradiate
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    direct high energy particles or radiation against
    type of:
    process, treat
    subject to a process or treatment, with the aim of readying for some purpose, improving, or remedying a condition
  7. noun
    a branch of an umbel or an umbelliform inflorescence
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    type of:
    pedicel, pedicle
    a small stalk bearing a single flower of an inflorescence; an ultimate division of a common peduncle
  8. noun
    the syllable naming the second (supertonic) note of any major scale in solmization
    synonyms: re
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    type of:
    solfa syllable
    one of the names for notes of a musical scale in solmization
  9. noun
    any of the stiff bony spines in the fin of a fish
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    type of:
    a sharp rigid animal process or appendage; as a porcupine quill or a ridge on a bone or a ray of a fish fin
  10. noun
    cartilaginous fishes having horizontally flattened bodies and enlarged winglike pectoral fins with gills on the underside; most swim by moving the pectoral fins
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    crampfish, electric ray, numbfish, torpedo
    any sluggish bottom-dwelling ray of the order Torpediniformes having a rounded body and electric organs on each side of the head capable of emitting strong electric discharges
    primitive ray with sharp teeth on each edge of a long flattened snout
    primitive tropical bottom-dwelling ray with a guitar-shaped body
    large venomous ray with large barbed spines near the base of a thin whiplike tail capable of inflicting severe wounds
    eagle ray
    powerful free-swimming tropical ray noted for `soaring' by flapping winglike fins; usually harmless but has venomous tissue near base of the tail as in stingrays
    devilfish, manta, manta ray
    extremely large pelagic tropical ray that feeds on plankton and small fishes; usually harmless but its size make it dangerous if harpooned
    large edible rays having a long snout and thick tail with pectoral fins continuous with the head; swim by undulating the edges of the pectoral fins
    Pristis pectinatus, smalltooth sawfish
    commonly found in tropical bays and estuaries; not aggressive
    Dasyatis centroura, roughtail stingray
    one of the largest stingrays; found from Cape Cod to Cape Hatteras
    butterfly ray
    a stingray with a short tail and a broad fin
    Aetobatus narinari, spotted eagle ray, spotted ray
    ray with back covered with white or yellow spots; widely distributed in warm seas
    Rhinoptera bonasus, cow-nosed ray, cownose ray
    large ray found along eastern coast of North America
    Atlantic manta, Manta birostris
    largest manta (to 22 feet across wings); found worldwide but common in Gulf of Mexico and along southern coasts of United States; primarily oceanic
    Mobula hypostoma, devil ray
    small manta (to 4 feet) that travels in schools
    Raja batis, gray skate, grey skate
    common European skate used as food
    Raja erinacea, little skate
    most plentiful skate in North American inshore waters in summer; to 21 inches
    Raja radiata, thorny skate
    cold-water bottom fish with spines on the back; to 40 inches
    Raja laevis, barndoor skate
    one of the largest skates (to 5 feet); an active skate easy to hook
    type of:
    elasmobranch, selachian
    any of numerous fishes of the class Chondrichthyes characterized by a cartilaginous skeleton and placoid scales: sharks; rays; skates
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