The Collaborative International Dictionary of English v.0.48:

Soy \Soy\ (soi), Soya \Soy"a\(soi"[.a]), n. [Chinese
   sh[=o]y[=u].]
   1. A Chinese and Japanese liquid sauce for fish, etc., made
      by subjecting boiled beans (esp. soybeans), or beans and
      meal, to long fermentation and then long digestion in salt
      and water.
      [1913 Webster]

   2. (Bot.) The soybean.
      [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Soybean \Soy"bean\ (soi"b[=e]n`), n.
   1. (Bot.) An Asiatic leguminous herb (Glycine max, formerly
      Glycine Soja) the seeds of which (also called soy
      beans) are used in preparing the sauce called soy.
      Called also soya bean and soya.
      [1913 Webster]

   2. the seeds of the Glycine max, which produce soybean
      oil; -- called also soya bean.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Soybean oil \Soy"bean oil\ (soi"b[=e]n` oil), n.
   an oil obtained from the soybean (Glycine max), rich in
   protein, fats, sterols, and phospholipids, used as a food and
   in paints and varnishes and in various industrial
   applications; -- called also soya oil. It is also used in
   preparing the sauce called soy or soy sauce.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Soja \So"ja\ (s[=o]"j[.a] or s[=o]"y[.a]), n. (Bot.)
   An Asiatic leguminous herb (Glycine max, formerly Glycine
   Soja) the seeds of which (called soy beans) are used in
   preparing the sauce called soy. Called also soya.
   [1913 Webster]

WordNet (r) 3.0 (2006):

soy
    n 1: a source of oil; used for forage and soil improvement and
         as food [syn: soy, soybean, soya bean]
    2: erect bushy hairy annual herb having trifoliate leaves and
       purple to pink flowers; extensively cultivated for food and
       forage and soil improvement but especially for its nutritious
       oil-rich seeds; native to Asia [syn: soy, soya,
       soybean, soya bean, soybean plant, soja, soja bean,
       Glycine max]
    3: thin sauce made of fermented soy beans [syn: soy sauce,
       soy]
    4: the most highly proteinaceous vegetable known; the fruit of
       the soybean plant is used in a variety of foods and as fodder
       (especially as a replacement for animal protein) [syn: soy,
       soybean, soya, soya bean]