1. Physics. A measure of the rate of rotational spin in a fluid.
2. Meteorology. A measure of the spin of an air mass such as a low- or high-pressure weather system.

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.