We don't have synonyms for sennas yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are senas, senna and sennar.
(n) :
(uncountable) The dried leaves or pods of these plants (especially of Senna alexandrina, syn. Cassia angustifolia or Cassia acutifolia), used medicinally.
(n) :
(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.
(n) :
(uncountable) The dried leaves or pods of these plants (especially of Senna alexandrina, syn. Cassia angustifolia or Cassia acutifolia), used medicinally.
(n) :
(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.