a. The hard outer portion or surface area of bread.
b. A piece of bread consisting mostly of the hard outer portion.
c. A piece of bread that has become hard and dry.
2. A pastry shell, as of a pie or tart.
3. A hard crisp covering or surface: snow with a firm crust.
4. A hard deposit formed on the interior of a wine bottle as the wine matures.
a. The solid, outermost layer of the earth, lying above the mantle.
b. The outermost solid layer of a planet or moon.
6. The hard outer covering or integument of certain plants and animals, such as lichens and crustaceans.
7. An outer layer or coating formed by the drying of a bodily exudate such as pus or blood; a scab.
8. Informal Insolence; audacity; gall.
v. crust·ed, crust·ing, crusts
1. To cover with a crust.
2. To form into a crust.
1. To become covered with a crust.
2. To harden into a crust.
[Middle English cruste, from Old French crouste, from Latin crusta; see kreus- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.