The Collaborative International Dictionary of English v.0.48:

Madwort \Mad"wort`\, n. (Bot.)
   A genus of cruciferous plants (Alyssum) with white or
   yellow flowers and rounded pods. Alyssum maritimum is the
   commonly cultivated sweet alyssum, a fragrant white-flowered
   annual.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Alyssum \A*lys"sum\ ([.a]*l[i^]s"s[u^]m), n. [NL., fr. Gr.
   'a`lysson, name of a plant, perh. fr. 'a priv. + ly`ssa
   raging madness.] (Bot.)
   A genus of cruciferous plants; madwort. The sweet alyssum
   (Alyssum maritimum), cultivated for bouquets, bears small,
   white, sweet-scented flowers.
   [1913 Webster]