pro·phy·lac·tic (prō′fə-lăktĭk, prŏf′ə-)
Acting to defend against or prevent something, especially disease; protective.
1. A prophylactic agent, device, or measure, such as a vaccine or drug.
2. A contraceptive device, especially a condom.
[French prophylactique, from Greek prophulaktikos, from prophulassein, to take precautions against : pro-, before; see PRO-2 + phulassein, to protect (from phulax, guard).]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. 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.