"walking on the whole sole of the foot" (opposed to digitigrade), 1831, from French plantigrade "walking on the sole of the foot" (1795), from Latin planta "sole of the foot" (from nasalized form of PIE root *plat- "to spread") + gradi "to walk, go, step" (from PIE root *ghredh- "to walk, go"). Used of man and other quadrupeds (bears, etc.) whose heels touch the ground in walking.
