n. pl. eight·ies
1. The cardinal number equal to 8 × 10.
a. A decade or the numbers from 80 to 89: They were still active in their eighties. Before noon, the temperature shot into the eighties.
b. often Eighties The decade from 80 to 89 in a century.
[Middle English eighti, from Old English eahtatig; see oktō(u) in the Appendix of Indo-European roots.]
eighty adj. & pron.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. 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.