NOUN (3)

1. a lightweight handheld collapsible canopy;

2. a formation of military planes maintained over ground operations or targets;
- Example: "an air umbrella over England"

3. having the function of uniting a group of similar things;
- Example: "the Democratic Party is an umbrella for many liberal groups"
- Example: "under the umbrella of capitalism"


ADJECTIVE (1)

1. covering or applying simultaneously to a number of similar items or elements or groups;
- Example: "an umbrella organization"
- Example: "umbrella insurance coverage"

The Collaborative International Dictionary of English v.0.48:

Umbrella \Um*brel"la\, n. [It. ombrella, fr. ombra a shade, L.
   umbra; cf. L. umbella a sunshade, a parasol. Cf. Umbel,
   Umbrage.]
   1. 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.
      [1913 Webster]

            Underneath the umbrella's oily shed.  --Gay.
      [1913 Webster]

   2. (Zool.) The umbrellalike disk, or swimming bell, of a
      jellyfish.
      [1913 Webster]

   3. (Zool.) Any marine tectibranchiate gastropod of the genus
      Umbrella, having an umbrella-shaped shell; -- called
      also umbrella shell.
      [1913 Webster]

   Umbrella ant (Zool.), the sauba ant; -- so called because
      it carries bits of leaves over its back when foraging.
      Called also parasol ant.

   Umbrella bird (Zool.), a South American bird
      (Cephalopterus ornatus) of the family Cotingidae. 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.

   Umbrella leaf (Bot.), an American perennial herb
      (Dyphylleia cymosa), having very large peltate and lobed
      radical leaves.

   Umbrella shell. (Zool.) See Umbrella, 3.

   Umbrella tree (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).
      [1913 Webster] Umbrere

WordNet (r) 3.0 (2006):

umbrella
    adj 1: covering or applying simultaneously to a number of
           similar items or elements or groups; "an umbrella
           organization"; "umbrella insurance coverage"
    n 1: a lightweight handheld collapsible canopy
    2: a formation of military planes maintained over ground
       operations or targets; "an air umbrella over England"
    3: having the function of uniting a group of similar things;
       "the Democratic Party is an umbrella for many liberal
       groups"; "under the umbrella of capitalism"

Moby Thesaurus II by Grady Ward, 1.0:

106 Moby Thesaurus words for "umbrella":
   aegis, agency, air cover, air raid, air support, arm guard, awning,
   backstop, beach umbrella, blind, bombing, brolly, buffer, bulwark,
   bumbershoot, bumper, chute, contraceptive, copyright, cover,
   coverage, crash helmet, curtain, cushion, dashboard, dodger, drape,
   drapery, drogue chute, dry run, face mask, fender, finger guard,
   foot guard, fuse, gamp, goggles, governor, guard, guardrail,
   hand guard, handrail, hard hat, harness, helmet, insulation,
   interlock, knee guard, knuckle guard, laminated glass,
   life preserver, lifeline, light shield, lightning conductor,
   lightning rod, mask, milk run, mission, mudguard, nose guard, pack,
   pad, padding, palladium, parachute, parachute jump, parasol,
   patent, patronage, pilot, preventive, prophylactic, protection,
   protective clothing, protective umbrella, reconnaissance,
   reconnaissance mission, safeguard, safety, safety glass,
   safety plug, safety rail, safety shoes, safety switch,
   safety valve, scramble, screen, seat belt, shade, shader, shadow,
   shield, shin guard, shroud lines, shuttle raid, sky dive, sortie,
   strafing, sun helmet, sunblind, sunshade, training mission, veil,
   vent, windscreen, windshield