undersurface vs bilge

undersurface and bilge both are nouns.

Word	Noun	Adjective	Verb	Adverb
undersurface	Yes	No	No	No
bilge	Yes	No	Yes	No

As nouns, bilge is a hyponym of undersurface; that is, bilge is a word with a more specific, narrower meaning than undersurface:

Other hyponyms of undersurface include base, heel, sole, underbelly.

undersurface (noun)	bilge (noun)
the lower side of anything	where the sides of the vessel curve in to form the bottom
	water accumulated in the bilge of a ship

undersurface (verb)	bilge (verb)
	take in water at the bilge
	cause to leak