1. Characterized by or adhering to strict standards or methods; exacting and thorough: a rigorous study of the medication; a rigorous researcher.
a. Harsh, severe, or demanding: a rigorous taskmaster; a rigorous schedule.
b. Very unpleasant or inclement: a rigorous climate.
3. Adhering strictly to a belief or ideology; uncompromising or inflexible: a rigorous Catholic; a rigorous sense of correctness.
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.