'Underneath' definitions:

Definition of 'underneath'

adverb

On the lower or downward side; on the underside of; "a chest of drawers all scratched underneath"

adverb

Under or below an object or a surface; at a lower place or level; directly beneath; "we could see the original painting underneath"; "a house with a good foundation underneath"

Definition of 'Underneath'

From: GCIDE

Underneath \Un`der*neath"\, adv. [OE. undirnepe. See Under, and Beneath.] Beneath; below; in a lower place; under; as, a channel underneath the soil. [1913 Webster]
Or sullen mole, that runneth underneath. --Milton. [1913 Webster]

Definition of 'Underneath'

From: GCIDE

Underneath \Un`der*neath"\, prep. Under; beneath; below. [1913 Webster]
Underneath this stone lie As much beauty as could die. --B. Jonson. [1913 Webster]

Synonyms of 'underneath'

From: Moby Thesaurus

bed,
bedrock,
belly,
below,
beneath,
bottom,
bottom side,
breech,
buttocks,
clandestine,
covert,
downside,
fundament,
furtive,
hardpan,
hole-and-corner,
lower side,
lowest layer,
lowest level,
neath,
nether side,
nethermost level,
rock bottom,
sole,
stealthy,
subordinate to,
substratum,
surreptitious,
under,
under-the-table,
underbelly,
undercover,
underlayer,
underside