The Collaborative International Dictionary of English v.0.48:

Plantigrade \Plan"ti*grade\, a. [L. planta sole of the foot +
   gradi to walk: cf. F. plantigrade.] (Zool.)
   (a) Walking on the sole of the foot; pertaining to the
       plantigrades.
   (b) Having the foot so formed that the heel touches the
       ground when the leg is upright.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Plantigrade \Plan"ti*grade\, n. (Zool.)
   A plantigrade animal, or one that walks or steps on the sole
   of the foot, as man, and the bears.
   [1913 Webster]

WordNet (r) 3.0 (2006):

plantigrade
    adj 1: (of mammals) walking on the whole sole of the foot (as
           rabbits, raccoons, bears, and humans do) [ant:
           digitigrade]
    n 1: an animal that walks with the entire sole of the foot
         touching the ground as e.g. bears and human beings [syn:
         plantigrade mammal, plantigrade] [ant: digitigrade,
         digitigrade mammal]