Noun
comprising seed plants that produce an embryo with a single cotyledon and parallel-veined leaves: includes grasses and lilies and palms and orchids; divided into four subclasses or superorders: Alismatidae; Arecidae; Commelinidae; and Liliidae
Source: WordNetThe Cronquist system also recognised this order with eight families, but organized the order in the subclass Zingiberidae of the class Liliopsida ( monocotyledons ). Source: Internet