The Collaborative International Dictionary of English v.0.48:

Pharmacognosis \Phar`ma*cog*no"sis\, n. [Gr. fa`rmakon a drug +
   gnw^sis a knowing.]
   That branch of pharmacology which treats of unprepared
   medicines or simples; -- usually called pharmacognosy, and
   also pharmacography, and pharmacomathy.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pharmacognosy \Phar`ma*cog"no*sy\, n.
   1. Pharmacognosis.
      [1913 Webster]

   2. The study of the distribution of, methods for finding, and
      properties of medically useful agents in natural sources,
      especially plants.
      [PJC]