A-line definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
fitting close at the top and flaring at the bottom: said of a woman's dress, coat, skirt, etc.
A-line definition by American Heritage Dictionary
Having a fitted top and a flared bottom: an A-line dress.
Origin: From garments being shaped like a capital A.