noun

• (uncountable) The state or quality of being sound.
• (countable) The result or product of being sound.
• (logic) The property (of an argument) of not only being valid, but also of having true premises.
• (logic) The property of a logical theory that whenever a wff is a theorem then it must also be valid. Symbolically, letting T represent a theory within logic L, this can be represented as the property that whenever T⊢ϕ is true, then T⊨ϕ must also be true, for any wff φ of logic L.