umbrella

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A device for protection from the weather consisting of a collapsible, usually circular canopy mounted on a central rod.
• noun Something shaped like an umbrella.
• noun The gelatinous, rounded mass that makes up the major part of the medusa stage of most jellyfish and certain other cnidarians.
• noun Something that covers or protects.
• noun Air cover, especially during a military operation.

from The Century Dictionary.

• noun A portable shade, screen, or canopy which opens and folds, carried in the hand for the purpose of sheltering the person from the rays of the sun or from rain.
• noun In zoology: The gelatinous disk or swimming-bell of an acaleph, as a jellyfish, by the rhythmical contraction and expansion of which the creature swims, taken either with or without the velum.
• noun In conchology [NL. (Lamarck, 1809).] [capitalized] A genus of tectibranchiate or pleurobranchiate gastropods; the umbrella-shells, as U. umbellata. Also Ombrella. A limpet-like tectibranchiate gastropod of the genus Umbrella or family Umbrellidæ; an umbrella-shell.

from the GNU version of the Collaborative International Dictionary of English.

• noun A shade, screen, or guard, carried in the hand for sheltering the person from the rays of the sun, or from rain or snow. It is formed of silk, cotton, or other fabric, extended on strips of whalebone, steel, or other elastic material, inserted in, or fastened to, a rod or stick by means of pivots or hinges, in such a way as to allow of being opened and closed with ease. See parasol.
• noun (Zoöl.) The umbrellalike disk, or swimming bell, of a jellyfish.
• noun (Zoöl.) Any marine tectibranchiate gastropod of the genus Umbrella, having an umbrella-shaped shell; -- called also umbrella shell.
• noun (Zoöl.) the sauba ant; -- so called because it carries bits of leaves over its back when foraging. Called also parasol ant.
• noun (Zoöl.) a South American bird (Cephalopterus ornatus) of the family Cotingidæ. It is black, with a large and handsome crest consisting of a mass of soft, glossy blue feathers curved outward at the tips. It also has a cervical plume consisting of a long, cylindrical dermal process covered with soft hairy feathers. Called also dragoon bird.
• noun (Bot.) an American perennial herb (Dyphylleia cymosa), having very large peltate and lobed radical leaves.
• noun (Zoöl.) See Umbrella, 3.
• noun (Bot.) a kind of magnolia (Magnolia Umbrella) with the large leaves arranged in umbrellalike clusters at the ends of the branches. It is a native of Pennsylvania, Virginia, and Kentucky. Other plants in various countries are called by this name, especially a kind of screw pine (Pandanus odoratissimus).

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Cloth-covered frame used for protection against rain or sun.
• noun Generally, anything that provides protection.
• noun Something that covers a wide range of concepts, purposes, groups and etc.
• noun The main body of a jellyfish, excluding the tentacles.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun having the function of uniting a group of similar things
• noun a formation of military planes maintained over ground operations or targets
• noun a lightweight handheld collapsible canopy
• adjective covering or applying simultaneously to a number of similar items or elements or groups