So-lĭd'ĭ-ty, n.

n. [Fr. solidité, Pr. soliditat, It. solidità, Lat. soliditas.] 1. The state of being solid; density; consistency,—opposed to fluidity; fullness of matter,—opposed to hollowness; strength; soundness,—opposed to weakness or instability; the primary quality or affection of matter by which its particles exclude or resist all others. That which hinders the approach of two bodies moving one toward another, I call solidity. Locke.

2. Moral firmness; soundness; strength; validity; truth; certainty;—as opposed to weakness or fallaciousness; as, the solidity of arguments or reasoning; the solidity of principles, truths, or opinions.
3. (Geom.) The solid contents of a body; volume.

Syn.—Firmness; solidness; hardness; density; compactness; strength; soundness; validity; certainty.