Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio.
a sky covered with rows of small, fleecy, cirrocumulus or altocumulus clouds, suggesting the streaks on a mackerel's back
Used by arrangement with John Wiley & Sons, Inc.
noun Chiefly Northeastern U.S.The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
A sky covered with many small cirrocumulus or altocumulus clouds, resembling the markings found on a mackerel. Also called regionally buttermilk sky.