Source : Webster's Revised Unabridged Dictionary (1913)

Solidness \Sol"id*ness\, n.
   1. State or quality of being solid; firmness; compactness;
      solidity, as of material bodies.

   2. Soundness; strength; truth; validity, as of arguments,
      reasons, principles, and the like.

Source : WordNet®

solidness
     n 1: 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 [syn: {solid}]
     2: the consistency of a solid [syn: {solidity}] [ant: {porosity}]