Source : Webster's Revised Unabridged Dictionary (1913)

Jalap \Jal"ap\, n. [F., fr. Sp. jalapa; -- so called from
   Jalapa, a town in Mexico, whence it was first obtained.]
   (Med.)
   The tubers of the Mexican plant {Ipom[oe]a purga} (or
   {Exogonium purga}), a climber much like the morning-glory.
   The abstract, extract, and powder, prepared from the tubers,
   are well known purgative medicines. Other species of
   Ipom[oe]a yield several inferior kinds of jalap, as the {I.
   Orizabensis}, and {I. tuberosa}.

   {False jalap}, the root of {Mirabilis Jalapa}, four-o'clock,
      or marvel of Peru.