The Collaborative International Dictionary of English v.0.48:

Prunella \Pru*nel"la\, n. [NL., perhaps from G. br[ae]une
   quinsy, croup.] (Med.)
   (a) Angina, or angina pectoris.
   (b) Thrush.
       [1913 Webster]

   Prunella salt (Old Chem.), niter fused and cast into little
      balls.
      [1913 Webster] Prunella