1. Physics The rate or a measure of the rate of motion, especially:
a. Distance traveled divided by the time of travel.
b. The limit of this quotient as the time of travel becomes vanishingly small; the first derivative of distance with respect to time.
c. The magnitude of a velocity.
2. Swiftness of action: He wrote the first chapter with great speed.
a. The act of moving rapidly: finished the race in a burst of speed.
b. The state of being in rapid motion; rapidity: The river's speed made a rescue difficult.
4. A transmission gear or set of gears in a motor vehicle: What speed is the car in now?
a. A numerical expression of the sensitivity of a photographic film, plate, or paper to light.
b. The capacity of a lens to accumulate light at an appropriate aperture.
c. The length of time required or permitted for a camera shutter to open and admit light.
6. Slang A stimulant drug, especially amphetamine or methamphetamine.
7. Slang One that suits or appeals to a person's inclinations, skills, or character: Living in a large city is not my speed.
8. Archaic Prosperity; luck.
v. sped (spĕd) or speed·ed, speed·ing, speeds
a. To go, move, or proceed quickly: sped to the rescue.
b. To drive at a speed exceeding a legal limit: was speeding on the freeway.
2. To pass quickly: The days sped by. The months have sped along.
3. To move, work, or happen at a faster rate; accelerate: His pulse speeded up.
4. Slang To be under the influence of a stimulant drug.
a. To prove successful; prosper.
b. To get along in a specified manner; fare.
1. To cause to move or proceed quickly; hasten: no wind to speed the boat.
2. To increase the speed or rate of; accelerate. Often used with up: speed up a car; sped up production.
3. To further, promote, or expedite (a legal action, for example).
4. Archaic To help to succeed or prosper; aid.
At high speed: added a spoiler to the car to reduce lift when operating at speed.
up to speed
1. Operating at maximum speed. Producing something or performing at an acceptable rate or level.
2. Informal Fully informed; conversant: I'm not up to speed on these issues yet.
[Middle English spede, from Old English spēd, success, swiftness; see spē- in the Appendix of Indo-European roots.]
Synonyms: speed, hurry, hasten, quicken, accelerate
These verbs mean to proceed or cause to proceed rapidly or more rapidly. Speed refers to swift motion or action: The train sped through the countryside. Postal workers labored overtime to speed delivery of the holiday mail. Hurry implies a markedly faster rate than usual, often with concomitant confusion or commotion: Hurry, or you'll miss the plane! Don't let anyone hurry you into making a decision. Hasten suggests urgency and often eager or rash swiftness: My doctor hastened to reassure me that the tests were negative. His off-color jokes only hastened his dismissal. Quicken and especially accelerate refer to increase in rate of activity, growth, or progress: The skater's breathing quickened as he neared the end of his routine. The runner quickened her pace as she drew near the finish line. The economic expansion has continued but is no longer accelerating. Heat greatly accelerates the deterioration of perishable foods. See Also Synonyms at haste.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.