The Collaborative International Dictionary of English v.0.48:

Marjoram \Mar"jo*ram\ (m[aum]r"j[-o]*ram), n. [OE. majoran, F.
   marjolaine, LL. marjoraca, fr. L. amaracus, amaracum, Gr.
   'ama`rakos, 'ama`rakon.] (Bot.)
   A genus of mintlike plants (Origanum) comprising about
   twenty-five species. The sweet marjoram (Origanum Majorana)
   is pecularly aromatic and fragrant, and much used in cookery.
   The wild marjoram of Europe and America is Origanum
   vulgare, far less fragrant than the other.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Origanum majorana
    n 1: aromatic European plant native to Mediterranean and Turkey;
         not widespread in Europe [syn: sweet marjoram, knotted
         marjoram, Origanum majorana, Majorana hortensis]