Black Death? (6)
I believe the answer is:
plague
'black death?' is the definition.
(black death is a kind of plague)
This is all the clue.
(Other definitions for plague that I've seen before include "Pester with deadly disease" , "Outbreak of a deadly disease, or infestation of pest like locusts" , "Deadly epidemic" , "Contagious disease that spreads rapidly and kills many" , "Epidemic disease with a high death rate" .)