1. Geology the solid outer shell of the earth, with an average thickness of 30--35 km in continental regions and 5 km beneath the oceans, forming the upper part of the lithosphere and lying immediately above the mantle, from which it is separated by the Mohorovicić discontinuity
2. the dry covering of a skin sore or lesion; scab
3. Oenology a layer of acid potassium tartrate deposited by some wine, esp port, on the inside of the bottle
4. Biology the hard outer layer of such organisms as lichens and crustaceans
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
crust The outermost solid layer of a terrestrial planet or a satellite, consisting of rock, ice, or a mixture of the two. See also Earth.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
in plants, a complex of tissues on the surface of the stem and roots of woody plants, consisting of dead peridermal cells and parts of the bark. The crust forms as layers of periderm repeatedly form in the phloem. In the case of more or less concentric arrangement of peridermal layers, a ringed crust forms (as in mock orange and grapes); if the peridermal layers overlap, a scaly crust forms (as in oak). Depending on the nature of the depositing of crust, it falls from the surface of the tree in layers, ribbons, or scales. Crust usually forms late (in birch, pine, and oak when the tree is 25–35 years old); it protects the plant from excessive evaporation, sharp fluctuations of temperature, and other undesirable effects.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
The outermost solid layer of the earth, mostly consisting of crystalline rock and extending no more than a few miles from the surface to the Mohorovičić discontinuity. Also known as earth crust.
A hard layer of snow lying on top of a soft layer.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.