quan·tum (kwŏn'təm)
n., pl., -ta (-tə).

1. A quantity or amount.
2. A specified portion.
3. Something that can be counted or measured.
4. Physics.
   1. The smallest amount of a physical quantity that can exist independently, especially a discrete quantity of electromagnetic radiation.
   2. This amount of energy regarded as a unit.

adj.
Relating to or based upon quantum mechanics.

[Latin, from neuter of quantus, how great. See quantity.]

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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.

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