umbrella

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A device for protection from the weather consisting of a collapsible, usually circular canopy mounted on a central rod.
2. n. Something that covers or protects.
3. n. Air cover, especially during a military operation.
4. n. Something that encompasses or covers many different elements or groups.
5. n. Zoology The gelatinous, rounded mass that is the major part of the body of most jellyfish.

Century Dictionary and Cyclopedia

1. n. 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. The name was formerly given to a sort of fan used to protect the face from the sun, but is now applied to a light canopy of silk, cotton, or other cloth, extended on a folding frame composed of bars or strips of steel, cane, etc., which slides on a rod or stick. A small and light form of umbrella, carried by women as a protection from the rays of the sun, often in gay colors, or ornamented with ribbons, lace, etc., is habitually called a parasol. The umbrella had its origin in very remote times in the far East, and in some Asiatic countries it was (and still is) regarded as an emblem of royalty or a mark of distinction. In ancient Greece its use was familiar among women for protection from the sun, and it is frequently represented in vase-paintings and terra-cottas. As a defense from rain or snow it was not used in western Europe till early in the eighteenth century. The word is sometimes used figuratively. Compare cloak.
2. n. 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. It is usually the largest, most symmetrical, and most coherent part of the jellyfish, from which other parts hang like streamers, either around its margin or from the center of the under surface. If we compare this bell to a woman's sun-umbrella, lined as well as covered with silk, and having a fringe, then the outer or aboral surface is the exumbrella; the inner or under lining surface is the adumbrella, or adoral surface surrounding the mouth, from which large mouth-parts may hang in the position of the stick or handle of the umbrella; the ring of metal which slides up and down the stick may represent the gastric cavity of the creature, and the metal ribs of the umbrella may suggest the radial canals which go out to the circumference. At points around the margin are the series of adradial, perradial, and interradial sense-organs or other appendages, as tentacles, and where these are long and streaming they represent the fringe of the imagined parasol. See cuts under acaleph, Aurelia, Discophora. and Willsia.
3. n. 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.

Wiktionary

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

GNU Webster's 1913

1. n. 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.
2. n. (Zoöl.) The umbrellalike disk, or swimming bell, of a jellyfish.
3. n. (Zoöl.) Any marine tectibranchiate gastropod of the genus Umbrella, having an umbrella-shaped shell; -- called also umbrella shell.

WordNet 3.0

1. n. having the function of uniting a group of similar things
2. n. a formation of military planes maintained over ground operations or targets
3. n. a lightweight handheld collapsible canopy
4. adj. covering or applying simultaneously to a number of similar items or elements or groups