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 Ipomœa 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 Ipomœa 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.