supergiant definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
an immense and extremely luminous star, as Betelgeuse or Antares, that has a diameter at least 100 times that of the sun and that is 100 to more than 10,000 times as bright
supergiant definition by American Heritage Dictionary
The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Any of various very large bright stars, such as Betelgeuse or Rigel, having a luminosity that is thousands of times greater than that of the sun.
supergiant - Science Definition
A star that is larger, brighter, and more massive than a giant star, being thousands of times brighter than the Sun and having a relatively short lifespan—only about 10 to 50 million years as opposed to around 5 billion years for the Sun. Supergiants, such as Betelgeuse and Rigel in Orion, are only found in young cosmic structures such as the arms of spiral galaxies. Red supergiants such as Betelgeuse are late-stage stars, having burned most of their hydrogen in an earlier stage as main-sequence stars, and now fuse helium into heavier elements through the triple alpha process. Blue supergiants such as Rigel are thought to have evolved from red giants, though some are considered main-sequence stars. Supergiants are thought to eventually undergo a supernova, ending up as neutron stars or black holes.