Source : Webster's Revised Unabridged Dictionary (1913)

Hayrack \Hay"rack`\, n.
   A frame mounted on the running gear of a wagon, and used in
   hauling hay, straw, sheaves, etc.; -- called also {hay
   rigging}.

Source : WordNet®

hayrack
     n 1: a rack that holds hay for feeding livestock
     2: a frame attached to a wagon to increase the amount of hay it
        can carry [syn: {hayrig}]