A head of iceberg lettuce.
iceberg lettuce 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.
variety of lettuce with crisp, medium-green leaves tightly folded into a round, compact head
iceberg lettuce definition by American Heritage Dictionary
A crisp, round, compact head of lettuce with light green, tightly folded leaves.
Origin: From its pale color.