1. Harmful to living things; injurious to health: noxious chemical wastes.
2. Harmful to the mind or morals; corrupting: noxious ideas.
[Middle English noxius, from Latin, from noxa, damage; see nek-1 in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.