The Collaborative International Dictionary of English v.0.48:

Hibiscus \Hi*bis"cus\, n. [L., marsh mallow; cf. Gr. ?.] (Bot.)
   A genus of plants (herbs, shrubs, or trees), some species of
   which have large, showy flowers. Some species are cultivated
   in India for their fiber, which is used as a substitute for
   hemp. See Althea, Hollyhock, and Manoe.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hibiscus
    n 1: any plant of the genus Hibiscus