Definition of "Solidness" :

noun: the quality of being solid and reliable financially or factually or morally

"The solidness of her faith gave her enduring hope."

noun: the quality of being substantial or having substance

noun: the consistency of a solid

noun: 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