The Collaborative International Dictionary of English v.0.48:

Gridiron \Grid"i`ron\, n. [OE. gredire, gredirne, from the same
   source as E. griddle, but the ending was confused with E.
   iron. See Griddle.]
   1. A grated iron utensil for broiling flesh and fish over
      coals.
      [1913 Webster]

   2. (Naut.) An openwork frame on which vessels are placed for
      examination, cleaning, and repairs.

   3. (Sport) A football field; -- so called because of the
      resemblance of the parallel marked yard lines to a
      gridiron[1].
      [PJC]

   Gridiron pendulum. See under Pendulum.

   Gridiron valve (Steam Engine), a slide valve with several
      parallel perforations corresponding to openings in the
      seat on which the valve moves.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gridiron
    n 1: a cooking utensil of parallel metal bars; used to grill
         fish or meat [syn: grid, gridiron]
    2: the playing field on which football is played [syn: football
       field, gridiron]