1. The cardinal number equal to 8 × 10.
2. eighties
   1. A decade or the numbers from 80 to 89: They were still active in their eighties. Before noon, the temperature shot into the eighties.
   2. often Eighties The decade from 80 to 89 in a century.

[Middle English eighti, from Old English eahtatig.]

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.