The Collaborative International Dictionary of English v.0.48:

Calendula \Ca*len"du*la\, n. [NL., fr. L. calendae calends.]
   (Bot.)
   A genus of composite herbaceous plants. One species,
   Calendula officinalis, is the common marigold, and was
   supposed to blossom on the calends of every month, whence the
   name.
   [1913 Webster]

WordNet (r) 3.0 (2006):

calendula
    n 1: any of numerous chiefly annual herbs of the genus Calendula
         widely cultivated for their yellow or orange flowers; often
         used for medicinal and culinary purposes