pestilence

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A usually fatal epidemic disease, especially bubonic plague.
• noun A pernicious, evil influence or agent.

from The Century Dictionary.

• noun The disease called the plague or pest; also, any epidemic malignant disease.
• noun That which is pestilential or pestiferous; that which produces or tends to produce malignant disease.
• noun That which is morally pestilent; that which is mischievous, noxious, or malignant in any respect.

from the GNU version of the Collaborative International Dictionary of English.

• noun Specifically, the disease known as the plague; hence, any contagious or infectious epidemic disease that is virulent and devastating.
• noun Fig.: That which is pestilent, noxious, or pernicious to the moral character of great numbers.
• noun (Bot.) the butterbur coltsfoot (Petasites vulgaris), so called because formerly considered a remedy for the plague.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any epidemic disease that is highly contagious, infectious, virulent and devastating.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a serious (sometimes fatal) infection of rodents caused by Yersinia pestis and accidentally transmitted to humans by the bite of a flea that has bitten an infected animal
• noun a pernicious and malign influence that is hard to get rid of
• noun any epidemic disease with a high death rate