(1):

(n.) The state or quality of being solid; density; consistency, - opposed to fluidity; compactness; fullness of matter, - opposed to openness or hollowness; strength; soundness, - opposed to weakness or instability; the primary quality or affection of matter by which its particles exclude or resist all others; hardness; massiveness.

(2):

(n.) Moral firmness; soundness; strength; validity; truth; certainty; - as opposed to weakness or fallaciousness; as, the solidity of arguments or reasoning; the solidity of principles, triuths, or opinions.

(3):

(n.) The solid contents of a body; volume; amount of inclosed space.