The Collaborative International Dictionary of English v.0.48:

Meadowsweet \Mead"ow*sweet`\, Meadowwort \Mead"ow*wort`\, n.
   (Bot.)
   The name of several plants of the genus Spiraea, especially
   the white- or pink-flowered Spiraea salicifolia, a low
   European and American shrub, and the herbaceous Spiraea
   Ulmaria, which has fragrant white flowers in compound cymes.
   [1913 Webster]