Easton's Bible Dictionary
Hebrews deber, "destruction," a "great mortality", the fifth plague that fell upon the Egyptians (Exodus 9:3). It was some distemper that resulted in the sudden and widespread death of the cattle. It was confined to the cattle of the Egyptians that were in the field (9:6).
Noah Webster's New International Dictionary of the English Language
1. (n.) An infectious and fatal disease among cattle.
2. (a.) Having, or afflicted with, murrain.