1. The cardinal number equal to 5 × 10.
a. A decade or the numbers from 50 to 59: They began playing golf in their fifties. With the sunshine, the temperature reached the fifties.
b. often Fifties The decade from 50 to 59 in a century.
3. A fifty-dollar bill.
[Middle English fifti, from Old English fīftig; see penkwe in the Appendix of Indo-European roots.]
fifty adj. & pron.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 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.