not sound; unhealthy, diseased, or disordered, as the body or mind.

decayed or impaired, as timber or foods; defective.

not solid or firm, as foundations.

not well-founded or valid; fallacious

an unsound argument.

easily broken; light

unsound slumber.

not financially strong; unreliable

an unsound corporation.

noun

debility , decrepitude , delicacy , delicateness , feebleness , flimsiness , fragileness , fragility , frailness , frailty , insubstantiality , puniness , unsubstantiality , weakliness , weakness