Definition of "senna"

(countable) Any of several plants of the tribe Cassieae, especially those of the genera Cassia and Senna, whose leaves and pods are used as a purgative and laxative.  examples

(uncountable) The dried leaves or pods of these plants (especially of Senna alexandrina, syn. Cassia angustifolia or Cassia acutifolia), used medicinally.  examples

(medicine) senna glycoside, a laxative.  examples