1. Any of the four angles formed between two straight lines intersected by a third straight line.
2. An angle formed inside a polygon by two adjacent sides.
(click for a larger image)interior angle
Angles 3, 4, 5, and 6 are interior angles. Angles 3 and 6 are alternate interior angles, as are angles 4 and 5.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. 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.