What's Trending Now
More Trending Words
principal section
noun
Definition of principal section
1 : a plane passing through the optical axis of a crystal; specifically : the principal plane that contains either the wave normal or the ray of light under discussion
2 : a plane perpendicular to the edge of an optical prism
Indulge Your Inner Word Nerd
There's more!
Love words? You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.
Start your free trial today and get unlimited access to America's largest dictionary, with:
- More than 250,000 words that aren't in our free dictionary
- Expanded definitions, etymologies, and usage notes
- Advanced search features
- Ad free!
Seen and Heard
What made you want to look up principal section? Please tell us where you read or heard it (including the quote, if possible).
Writing? Check your grammar now!