Portuguese man-of-war 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.
any of a genus (Physalia) of large, colonial, warm-sea siphonophores having a large, bladderlike sac, with a sail-like structure on top, which enables them to float on the water, and long, dangling tentacles that have powerful stinging cells
Portuguese man-of-war definition by American Heritage Dictionary
A complex colonial siphonophore of the genus Physalia, of warm seas, having a bluish bladderlike float with a broad saillike crest from which hang numerous long stinging tentacles.