The Collaborative International Dictionary of English v.0.48:

Cubic \Cu"bic\, n. (Geom.)
   A curve of the third degree.
   [1913 Webster]

   Circular cubic. See under Circular.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cubic \Cu"bic\ (k?"b?k), Cubical \Cu"bic*al\ (-b?-kal), a. [L.
   cubicus, Gr. ?????: cf. F. cubique. See Cube.]
   1. Having the form or properties of a cube; contained, or
      capable of being contained, in a cube.
      [1913 Webster]

   2. (Crystallog.) Isometric or monometric; as, cubic cleavage.
      See Crystallization.
      [1913 Webster]

   Cubic equation, an equation in which the highest power of
      the unknown quantity is a cube.

   Cubic foot, a volume equivalent to a cubical solid which
      measures a foot in each of its dimensions.

   Cubic number, a number produced by multiplying a number
      into itself, and that product again by the same number.
      See Cube.

   Cubical parabola (Geom.), two curves of the third degree,
      one plane, and one on space of three dimensions.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cubic
    adj 1: having three dimensions [syn: cubic, three-
           dimensional] [ant: linear, one-dimensional,
           planar, two-dimensional]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "cubic":
   3-D, cube-shaped, cubed, cubiform, cuboid, diced, dimensional,
   flat, foursquare, fourth-dimensional, oblong, orthogonal,
   proportional, quadrangular, quadrate, quadriform, quadrilateral,
   rectangular, rhombic, rhomboid, space, space-time, spatial,
   spatiotemporal, spherical, square, stereoscopic, superficial,
   surface, tetragonal, tetrahedral, three-dimensional, trapezohedral,
   trapezoid, two-dimensional, volumetric