The Collaborative International Dictionary of English v.0.48:

Lawsonia \Law*so"ni*a\, n. (Bot.)
   An Asiatic and North African shrub (Lawsonia inermis), with
   smooth oval leaves, and fragrant white flowers. Henna is
   prepared from the leaves and twigs. In England the shrub is
   called Egyptian privet, and in the West Indies, Jamaica
   mignonette.
   [1913 Webster]