a genus of leguminous plants (herbs, shrubs, or trees) of many species, most of which have purgative qualities. the leaves of several species furnish the senna used in medicine.-the bark of several species of cinnamomum grown in china, etc.; chinese cinnamon.  it is imported as cassia, but commonly sold as cinnamon, from which it differs more or less in strength and flavor, and the amount of outer bark attached.