from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. infrared
from the GNU version of the Collaborative International Dictionary of English
- adj. Situated beyond or below the red rays.
from The Century Dictionary and Cyclopedia
- Beyond the red: used of the invisible heat-rays, less refrangible than those forming the lower or red part of the spectrum, more commonly called the infra-red rays. See spectrum.
ultra- + red (Wiktionary)