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a. A hat of cloth or straw, often held in place by ribbons tied under the chin and traditionally worn by women and children.
b. Scots A brimless cap traditionally worn by men or boys.
2. A removable metal plate over a machine part, such as a valve.
3. Chiefly British The hood of an automobile.
a. A windscreen for a chimney.
b. A cover for a fireplace.
5. Nautical A strip of canvas laced to a fore-and-aft sail to increase sail area.
tr.v. bon·net·ed, bon·net·ing, bon·nets
To put a bonnet on.

[Middle English bonet, cap, from Old French, material for a headdress, perhaps from Medieval Latin obbonis, probably of Germanic origin.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.