The Collaborative International Dictionary of English v.0.48:

Tracery \Tra"cer/y\, n.; pl. Traceries (Arch.)
   1. Ornamental work with rambled lines. Especially:
      (a) The decorative head of a Gothic window.
          [1913 Webster]

   Note: Window tracery is of two sorts, plate tracery and bar
         tracery. Plate tracery, common in Italy, consists of a
         series of ornamental patterns cut through a flat plate
         of stone. Bar tracery is a decorative pattern formed by
         the curves and intersections of the molded bars of the
         mullions. Window tracery is imitated in many decorative
         objects, as panels of wood or metal either pierced or
         in relief. See also Stump tracery under Stump, and
         Fan tracery under Fan.
         [1913 Webster]
      (b) A similar decoration in some styles of vaulting, the
          ribs of the vault giving off the minor bars of which
          the tracery is composed.
          [1913 Webster]

   2. A tracing of lines; a system of lines produced by, or as
      if by, tracing, esp. when interweaving or branching out in
      ornamental or graceful figures. "Knit with curious
      tracery." --Burns.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

tracery
    n 1: decoration consisting of an open pattern of interlacing
         ribs

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "tracery":
   arabesque, arc, basketry, basketwork, bow, cancellation,
   catacaustic, catenary, caustic, circle, conchoid, crook,
   cross-hatching, crossing-out, curl, curve, diacaustic, ellipse,
   festoon, filigree, fret, fretwork, grate, grating, grid, gridiron,
   grille, grillwork, hachure, hatching, hook, hyperbola,
   interlacement, intertexture, intertwinement, lace, lacery,
   lacework, lacing, lattice, latticework, lituus, mesh, meshes,
   meshwork, net, netting, network, parabola, plexure, plexus, raddle,
   reticle, reticulation, reticule, reticulum, riddle, screen,
   screening, sieve, sinus, texture, tissue, trellis, trelliswork,
   wattle, weave, weaving, web, webbing, webwork, weft, wicker,
   wickerwork