tr.v. ac·ti·vat·ed, ac·ti·vat·ing, ac·ti·vates
1. To set in motion; make active or more active.
2. To organize or create (a military unit, for example): activate the National Guard.
3. To treat (sewage) with aeration and bacteria to aid decomposition.
4. Chemistry To accelerate a reaction in, as by heat.
5. Physics To make (a substance) radioactive.
6. Biology To convert (a molecule or cell) into a form that carries out a specific action: activate an enzyme; activate B cells.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 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.