The name Senna is a girl's name of Arabic origin meaning "brightness". Senna and is often added to lists like Flower Names for Girls and discussed in our forums with posts like "Quick Question Thread?!".
From the experts:
Senna is a flowering bush common in the tropics, with bright yellow flowers. In herbal medicine, Senna has gained some notice as the active ingredient in so-called "dieter's teas," which works mainly as a laxative. While that is a less-than-savory association, Senna has a pretty sound and is a fresh entry in the flourishing botanical names genus.