The Collaborative International Dictionary of English v.0.48:

Gressorial \Gres*so"ri*al\, Gressorious \Gres*so"ri*ous\, a. [L.
   gressus, p. p. of gradi to step, go.] (Zool.)
   Adapted for walking; anisodactylous; as the feet of certain
   birds and insects. See Illust. under Aves. Gret