calendula(n = noun.plant) - 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;
is a kind of flower
is a member of genus calendula
has particulars: calendula officinalis, common marigold, pot marigold, ruddles, scotch marigold

   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]

calendula, n. any plant of the genus Calendula, with large yellow or orange flowers, e.g. marigold.

Etymology:
mod.L dimin. of calendae (as CALENDS), perh. = little clock

calendula officinalis, genus calendula, regulus calendula