The Collaborative International Dictionary of English v.0.48:

Petunia \Pe*tu"ni*a\ (p[-e]*t[=u]"n[i^]*[.a]), n. [NL., fr.
   Braz. petun tobacco.] (Bot.)
   A genus of solanaceous herbs with funnel-form or
   salver-shaped corollas. Two species are common in
   cultivation, Petunia violacea, with reddish purple flowers,
   and Petunia nyctaginiflora, with white flowers. There are
   also many hybrid forms with variegated corollas.
   [1913 Webster] Petuntse
   Petunse

WordNet (r) 3.0 (2006):

petunia
    n 1: any of numerous tropical herbs having fluted funnel-shaped
         flowers
    2: annual or perennial herbs or shrubs of tropical South America
       [syn: genus Petunia, Petunia]