Source : Webster's Revised Unabridged Dictionary (1913)

Underfoot \Un`der*foot"\, a.
   Low; base; abject; trodden down.

Underfoot \Un`der*foot"\, adv.
   Under the feet; underneath; below. See {Under foot}, under
   {Foot}, n.

Source : WordNet®

underfoot
     adv 1: under the feet; "trampled the beans underfoot"; "green grass
            growing underfoot"
     2: in the way and hindering progress; "a house with children
        and pets and toys always underfoot"