The Collaborative International Dictionary of English v.0.48:

Soundness \Sound"ness\, n.
   The quality or state of being sound; as, the soundness of
   timber, of fruit, of the teeth, etc.; the soundness of
   reasoning or argument; soundness of faith.
   [1913 Webster]

   Syn: Firmness; strength; solidity; healthiness; truth;
        rectitude.
        [1913 Webster]

WordNet (r) 3.0 (2006):

soundness
    n 1: a state or condition free from damage or decay [ant:
         unsoundness]
    2: the quality of being prudent and sensible [syn: wisdom,
       wiseness, soundness] [ant: unsoundness]
    3: the muscle tone of healthy tissue; "his muscular firmness"
       [syn: firmness, soundness] [ant: unsoundness]

Moby Thesaurus II by Grady Ward, 1.0:

196 Moby Thesaurus words for "soundness":
   admissibility, advantageousness, agreeableness, aplomb,
   auspiciousness, authenticity, authoritativeness, authority,
   balance, balanced personality, beneficialness, benevolence,
   benignity, body, calculability, canonicalness, canonicity, class,
   cogency, common sense, completeness, concreteness, constancy,
   contact with reality, cool, cool head, coolheadedness, coolness,
   credit standing, density, dependability, desert, due sense of,
   durability, entireness, equilibrium, eupepsia, excellence,
   expedience, fairness, faithworthiness, fastness, favorableness,
   fine fettle, fine shape, fine whack, fineness, firmness,
   first-rateness, force, fullness, glowing health, good condition,
   good constitution, good digestion, good health, good sense,
   good shape, good trim, goodliness, goodness, gospel truth, grace,
   haleness, hardness, healthfulness, healthiness, healthy body,
   healthy constitution, healthy mind, helpfulness, high feather,
   homeostasis, horse sense, imperturbability, intactness, integrity,
   invariability, invincibility, justifiability, justness, kindness,
   level head, level-headedness, levelheadedness, logic, logicality,
   logicalness, lucid interval, lucidity, marbles, mass, materiality,
   mental balance, mental equilibrium, mental health, mental hygiene,
   mental poise, merit, mind, mint condition, nerve, niceness,
   normalcy, normality, normalness, orthodoxicalness, orthodoxism,
   orthodoxness, orthodoxy, palpability, picture of health,
   plain sense, plausibility, pleasantness, plenitude, ponderability,
   practical mind, practical wisdom, practicality, predictability,
   profitableness, quality, rationality, reason, reasonability,
   reasonableness, reliability, religious truth, rewardingness,
   right belief, right mind, rightness, robust health, rootedness,
   rude health, rugged health, sanemindedness, saneness, sang-froid,
   sanity, secureness, security, sense, senses, sensibleness,
   skillfulness, sober senses, sober-mindedness, soberness, sobriety,
   solidity, solvency, sound mind, sound sense, soundness of mind,
   stability, stable equilibrium, stable state, stableness,
   staunchness, steadfastness, steadiness, steady nerves,
   steady state, stoutness, strength, sturdiness, substance,
   substantiality, substantialness, superiority, sweet reason,
   tangibility, temper, the truth, top shape, toughness,
   traditionalism, trustworthiness, undeflectability, unerringness,
   uniformity, unindebtedness, unshakable nerves, unshakableness,
   usefulness, validity, value, virtue, virtuousness, weight,
   wholeness, wholesomeness, wit, worth



The Free On-line Dictionary of Computing (30 December 2018):

soundness

   The quality of being sound (2).


Bouvier's Law Dictionary, Revised 6th Ed (1856):

SOUNDNESS. In usual health; without any permanent disease. 1 Carr. & Marsh.
291. To create unsoundness, it is requisite that the animal should not be
useful for the purpose for which he is bought, and that inability to be so
useful should arise from disease or accident. 2 M. & Rob. 137; 9 M. & W.
670. 2 M. & Rob. 113.
     2. In the sale of slaves and animals they are sometimes warranted by
the seller to be sound, and it becomes important to ascertain what is
soundness. Roaring; (q.v.) a temporary lameness, which renders a horse less
fit for service; 4 Campb. 271; sed vide 2 Esp. Cas. 573; a cough, unless
proved to be of a temporary nature; 2 Chit. R. 245, 416; and a nerved horse,
have been held to be unsound. But cribbiting is not a breach of a general
warranty of soundness. Holt, Cas. 630.
     3. An action on the case is the proper remedy for a verbal warrant of
soundness. 1 H. Bl. R. 17; 3 Esp. 82; 9 B. & Cr. 259; 2 Dow. & Ry. 10; 1
Bing. 344; 5 Dow. & R. 164; 1 Taunt. 566; 7 East, 274; Bac. Ab. Action on
the Case, E.