Source : Webster's Revised Unabridged Dictionary (1913)

Underneath \Un`der*neath"\, adv. [OE. undirnepe. See {Under},
   and {Beneath}.]
   Beneath; below; in a lower place; under; as, a channel
   underneath the soil.

         Or sullen mole, that runneth underneath. --Milton.

Underneath \Un`der*neath"\, prep.
   Under; beneath; below.

         Underneath this stone lie As much beauty as could die.
                                                  --B. Jonson.

Source : WordNet®

underneath
     adv 1: on the lower or downward side; "a chest of drawers all
            scratched underneath"
     2: lower down on the page; "diagrams with figures underneath"
     3: beneath by way of support; "a house with a good foundation
        underneath"
     4: under or below an object or a surface; "we could see the
        original painting underneath"