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):

marjoram
    n 1: aromatic Eurasian perennial [syn: oregano, marjoram,
         pot marjoram, wild marjoram, winter sweet, Origanum
         vulgare]
    2: pungent leaves used as seasoning with meats and fowl and in
       stews and soups and omelets [syn: marjoram, oregano]