1. The act of expanding or the state of being expanded.
2. Medicine. See dilatation (sense 2).
3. A lengthy spoken or written discussion on a topic: "an Edith Whartonesque dilation on a social class steeped in hypocrisy" (Caroline Seebohm).

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.