Easton's Dictionary
Occurs only in connection with the sixth plague of Egypt (Ex. 9:9, 10). In Deut. 28:27, 35, it is called “the botch of Egypt.”
It seems to have been the fearful disease of black leprosy, a
kind of elephantiasis, producing burning ulcers.
Smith's Dictionary
violent ulcerous inflammations, the sixth plague of Egypt, (Exodus 9:9,10) and hence called in (28:27,35) “the botch of Egypt.” It seems to have been the black leprosy, a fearful kind of elephantiasis.
International Standard Bible Encyclopedia
blanz (abha`bu`ah: only in Ex 9:9,10): Pustules containing fluid around a boil or inflamed sore. It is an Old English word "bleyen," used sometimes as a synonym for boil. Wyclif (1382) uses the expression "stinkende bleyne" for Job's sores. The Hebrew word is from a root which means that which bubbles up.
See BOIL.