The Collaborative International Dictionary of English v.0.48:

Damewort \Dame"wort`\, n. (Bot.)
   A cruciferrous plant (Hesperis matronalis), remarkable for
   its fragrance, especially toward the close of the day; --
   called also rocket and dame's violet. --Loudon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Hesperis matronalis
    n 1: long cultivated herb having flowers whose scent is more
         pronounced in the evening; naturalized throughout Europe to
         Siberia and into North America [syn: damask violet,
         Dame's violet, sweet rocket, Hesperis matronalis]