The Collaborative International Dictionary of English v.0.48:

Grade \Grade\ (gr[=a]d), n. [F. grade, L. gradus step, pace,
   grade, from gradi to step, go. Cf. Congress, Degree,
   Gradus.]
   1. A step or degree in any series, rank, quality, order;
      relative position or standing; as, grades of military
      rank; crimes of every grade; grades of flour.
      [1913 Webster]

            They also appointed and removed, at their own
            pleasure,
            teachers of every grade.              --Buckle.
      [1913 Webster]

   2. In a railroad or highway:
      (a) The rate of ascent or descent; gradient; deviation
          from a level surface to an inclined plane; -- usually
          stated as so many feet per mile, or as one foot rise
          or fall in so many of horizontal distance; as, a heavy
          grade; a grade of twenty feet per mile, or of 1 in
          264.
      (b) A graded ascending, descending, or level portion of a
          road; a gradient.
          [1913 Webster]

   3. (Stock Breeding) The result of crossing a native stock
      with some better breed. If the crossbreed have more than
      three fourths of the better blood, it is called high
      grade.
      [1913 Webster]

   At grade, on the same level; -- said of the crossing of a
      railroad with another railroad or a highway, when they are
      on the same level at the point of crossing.

   Down grade, a descent, as on a graded railroad.

   Up grade, an ascent, as on a graded railroad.

   Equating for grades. See under Equate.

   Grade crossing, a crossing at grade.
      [1913 Webster]

WordNet (r) 3.0 (2006):

grade crossing
    n 1: intersection of a railway and a road on the same level;
         barriers close road when trains pass [syn: level
         crossing, grade crossing]