The Collaborative International Dictionary of English v.0.48:

Jonquil \Jon"quil\, Jonquille \Jon"quille\, n. [F. jonquille,
   fr. L. juncus a rush, because it has rushlike leaves.] (Bot.)
   A bulbous plant of the genus Narcissus (Narcissus
   Jonquilla), allied to the daffodil. It has long, rushlike
   leaves, and yellow or white fragrant flowers. The root has
   emetic properties. It is sometimes called the rush-leaved
   daffodil. See Illust. of Corona.
   [1913 Webster]

WordNet (r) 3.0 (2006):

jonquil
    n 1: widely cultivated ornamental plant native to southern
         Europe but naturalized elsewhere having fragrant yellow or
         white clustered flowers [syn: jonquil, Narcissus
         jonquilla]
    2: often used colloquially for any yellow daffodil