unsubstantial vs hollow

unsubstantial is not a noun while hollow is a noun.

Word	Noun	Adjective	Verb	Adverb
unsubstantial	No	Yes	No	No
hollow	Yes	Yes	Yes	No

unsubstantial (noun)	hollow (noun)
	a depression hollowed out of solid matter
	a small valley between mountains
	a cavity or space in something

unsubstantial (adjective)	hollow (adjective)
lacking material form or substance; unreal	not solid; having a space or gap or cavity
	lacking in substance or character
	devoid of significance or force
	as if echoing in a hollow space

unsubstantial (verb)	hollow (verb)
	remove the interior of
	remove the inner part or the core of