n. pl. ac·tiv·i·ties
1. The state of being active.
2. Energetic action or movement; liveliness.
a. A specified pursuit in which a person partakes.
b. An educational process or procedure intended to stimulate learning through actual experience.
4. The intensity of a radioactive source.
5. The ability to take part in a chemical reaction.
6. A physiological process: respiratory activity.
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.