solidness vs unsubstantial

solidness is a noun but unsubstantial is not a noun.

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

solidness (noun)	unsubstantial (noun)
the quality of being substantial or having substance
the quality of being solid and reliable financially or factually or morally
the consistency of a solid
the state in which a substance has no tendency to flow under moderate stress; resists forces (such as compression) that tend to deform it; and retains a definite size and shape

solidness (adjective)	unsubstantial (adjective)
	lacking material form or substance; unreal