Definition of nitric oxide
: a colorless poisonous gas NO formed by oxidation of nitrogen or ammonia that is present in the atmosphere and also in mammals where it is synthesized from arginine and oxygen and acts as a vasodilator and as a mediator of cell-to-cell communication (as between nerve cells) — compare nitrous oxide
Keep scrolling for more
Keep scrolling for more
Test Your Vocabulary
Words of Snow and Ice Quiz
- Which of the following refers to thin, bending ice, or to the act of running over such ice?

Test your knowledge - and maybe learn something along the way.
TAKE THE QUIZ
Anagram puzzles meet word search.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridgedWords at Play
Ask the Editors
Word Games
Words of Snow and Ice Quiz
A selection of words from the chillier parts of t...
Take the quizName that Thing: Toys and Games Edition
It's all fun and games until someone beats your h...
Take the quizTrue or False?
Test your knowledge - and maybe learn something a...
Take the quizSCRABBLE® Sprint
SCRABBLE® fans, sharpen your skills!
Play the game
Share nitric oxide
Time Traveler for nitric oxide
The first known use of nitric oxide was in 1789
See more words from the same year