Speed most often describes acceleration or a high rate of motion. When something picks up too much speed, it can run off course, like a kid on a bike zooming uncontrollably down a steep hill.

Speed can be a noun or verb. As a noun, it's an indicator of pace, as in the speed of a car. As a noun, it's also a drug that keeps you awake, very awake. As a verb, it means to “move along quickly,” like how you speed around on your bike. A fun fact: while speed refers to the distance traveled by an object during a specific amount of time, velocity describes that distance, but in a specified direction.

Definitions of speed
  1. noun
    a rate (usually rapid) at which something happens
    “the project advanced with gratifying speed
    synonyms: fastness, swiftness
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    haste, hastiness, hurriedness, hurry, precipitation
    overly eager speed (and possible carelessness)
    execution speed
    (computer science) the speed with which a computational device can execute instructions; measured in MIPS
    graduality, gradualness
    the quality of being gradual or of coming about by gradual stages
    abruptness, precipitance, precipitancy, precipitateness, precipitousness, suddenness
    the quality of happening with headlong haste or without warning
    type of:
    clip, pace, rate
    the relative speed of progress or change
  2. noun
    distance travelled per unit time
    synonyms: velocity
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    angular velocity
    (physics) the rate of change of the angular position of a rotating body; usually expressed in radians per second or radians per minute
    the speed of an aircraft relative to the air in which it is flying
    escape velocity
    the minimum velocity needed to escape a gravitational field
    the speed of an aircraft relative to the ground
    excessive velocity
    muzzle velocity
    the velocity of a projectile as it leaves the muzzle of a gun
    peculiar velocity
    velocity with respect to the local standard of rest
    radial velocity
    velocity along the line of sight toward or away from the observer
    c, light speed, speed of light
    the speed at which light travels in a vacuum; the constancy and universality of the speed of light is recognized by defining it to be exactly 299,792,458 meters per second
    (nautical) the minimum rate of motion needed for a vessel to be maneuvered
    terminal velocity
    the constant maximum velocity reached by a body falling through the atmosphere under the attraction of gravity
    type of:
    a magnitude or frequency relative to a time unit
  3. noun
    changing location rapidly
    synonyms: hurrying, speeding
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    acceleration, quickening, speedup
    the act of accelerating; increasing the speed
    the act of decelerating; decreasing the speed
    scud, scudding
    the act of moving along swiftly (as before a gale)
    type of:
    motion, move, movement
    the act of changing location from one place to another
  4. verb
    move fast
    synonyms: belt along, bucket along, cannonball along, hasten, hie, hotfoot, pelt along, race, rush, rush along, step on it
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    dawdle, linger
    take one's time; proceed slowly
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    barge, push forward, thrust ahead
    push one's way
    buck, charge, shoot, shoot down, tear
    move quickly and violently
    dart, dash, flash, scoot, scud, shoot
    run or move very quickly or hastily
    dash violently or with great speed or impetuosity
    move precipitously or violently
    type of:
    go, locomote, move, travel
    change location; move, travel, or proceed, also metaphorically
  5. verb
    move faster
    synonyms: accelerate, quicken, speed up
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    decelerate, retard, slow, slow down, slow up
    lose velocity; move more slowly
    brisk, brisk up, brisken
    become brisk
    type of:
    deepen, intensify
    become more intense
  6. verb
    move very fast
    “The runner zipped past us at breakneck speed
    synonyms: hurry, travel rapidly, zip
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    dart, fleet, flit, flutter
    move along rapidly and lightly; skim or dart
    move fast by using one's feet, with one foot off the ground at any given time
    whizz, whizz along, zoom, zoom along
    move along very quickly
    flutter like a butterfly
    clip, jog, trot
    run at a moderately swift pace
    scamper, scurry, scuttle, skitter
    move about or proceed hurriedly
    run easily and fairly fast
    run bases
    run around the bases, in baseball
    run naked in a public place
    run with the ball; in such sports as football
    run faster than
    run for exercise
    run very fast, usually for a short distance
    run easily
    run with the ball, in football
    run quickly, like a hare
    type of:
    go, locomote, move, travel
    change location; move, travel, or proceed, also metaphorically
  7. verb
    travel at an excessive or illegal velocity
    “I got a ticket for speeding
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    type of:
    go, locomote, move, travel
    change location; move, travel, or proceed, also metaphorically
  8. verb
    cause to move faster
    synonyms: accelerate, speed up
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    decelerate, slow down
    reduce the speed of
    type of:
    alter, change, modify
    cause to change; make different; cause a transformation
  9. noun
    the ratio of the focal length to the diameter of a (camera) lens system
    synonyms: f number, focal ratio, stop number
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    type of:
    the relative magnitudes of two quantities (usually expressed as a quotient)
  10. noun
    a central nervous system stimulant that increases energy and decreases appetite; used to treat narcolepsy and some forms of depression
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    amphetamine sulfate, amphetamine sulphate
    a sulfate derivative of amphetamine that is used as a stimulant for the central nervous system
    Benzedrine, bennie
    a form of amphetamine
    Dexedrine, dextroamphetamine sulphate
    an isomer of amphetamine (trade name Dexedrine) used as a central nervous system stimulant
    type of:
    drug of abuse, street drug
    a drug that is taken for nonmedicinal reasons (usually for mind-altering effects); drug abuse can lead to physical and mental damage and (with some substances) dependence and addiction
    excitant, stimulant, stimulant drug
    a drug that temporarily quickens some vital process
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