a. The act of irritating: the prankster's irritation of the others in the dorm.
b. The condition of being irritated; vexation: honked the horn with irritation at the delay.
2. A source of irritation: Their constant talking is an irritation to people who are reading.
3. An inflammatory reaction of a bodily part.
4. Physiology The elicitation of a response to a stimulus in a plant or animal organ or tissue, especially in a nerve or muscle.
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.