The Collaborative International Dictionary of English v.0.48:

madonna lily \madonna lily\ n. (Bot.)
   A lily (Lilium candidum) of the Eastern Mediterranean and
   Balkans with broad funnel-shaped white flowers.

   Syn: white lily, Annunciation lily, Lent lily, Lilium
        candidum.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Madonna lily
    n 1: lily of eastern Mediterranean and the Balkans with broad
         funnel-shaped white flowers [syn: Madonna lily, white
         lily, Annunciation lily, Lent lily, Lilium candidum]