What is "pestilence weed"

Pestilence \Pes"ti*lence\, n. [F. pestilence, L. pestilentia. See Pestilent.]

1. Specifically, the disease known as the plague; hence, any contagious or infectious epidemic disease that is virulent and devastating.

   The pestilence That walketh in darkness.
   --Ps. xci. 6.

2. Fig.: That which is pestilent, noxious, or pernicious to the moral character of great numbers.

   I'll pour this pestilence into his ear.
   --Shak.

   Pestilence weed (Bot.), the butterbur coltsfoot ( Petasites vulgaris), so called because formerly considered a remedy for the plague.
   --Dr. Prior.