Synonyms for Unsound:

adj.

bad (adjective)
inferior, inadvisable, unsatisfactory, poor, unfavorable, ill-suited, detrimental, invalid, arrant, black, vile, unpleasant, wretched, defective, inadequate, bad, displeasing, irremediable, baneful, faulty, wrong.
daft (adjective)
screwy.
dangerous (adjective)
unsafe, perilous.
dishonest (adjective)
untrue.
erroneous (adjective)
inaccurate.
false (adjective)
erroneous, incongruous, false, illogical.
insane (adjective)
bananas, fruity, moonstruck, loco, brainsick, crackers.
not well; flimsy (adjective)
specious, defective, incorrect, unsubstantial, unbalanced, insubstantial, weak, infirm, incongruous, demented, erroneous, mad, fallacious, lunatic, inaccurate, frail, illogical, faulty, unstable, unsafe, insecure, dangerous, delicate, insane, invalid, decrepit, false, unreliable, fragile, unhealthy.
of unsound mind (adjective)
non compos mentis.
wrong (adjective)
incorrect.

n.

absurd, hysterical, irresponsible, perverse, ridiculous, childish, extreme. erroneous, inaccurate, mistaken, incorrect, untrue. false (noun)
erroneous, incongruous, false, illogical.
insecure (noun)
weak.
unsound (noun)
rotten, damaged, unhealthy, unstable, fallacious, dilapidated, invalid, decayed, long, wildcat, broken-down, undependable, insecure, tumble-down, bedraggled, rotted, unreliable, mentally ill, corroded, ramshackle, bad, speculative, insane, unfit, risky, high-risk, tatterdemalion.

v.

deranged (verb)
unbalanced.

Other synonyms:

crackers, sophistic, Daffy, weakly, bonkers, chancy, brainsick, dotty, fruity, touch-and-go, loco, bananas, batty. indiscreet, demented, inaccurate, cracked, frail, ill-considered, gaga, crazy, erroneous, injudicious, impolitic, unwise, maniacal, distraught, imprudent, wacky, nutty, puny, infirm, daft, decrepit, nuts, ill-advised, unsafe, bold, lunatic, screwy, mistaken, buggy, do-or-die, incorrect, loony, non compos mentis. disordered, feeble, flimsy, unsubstantial, untrue, brave, fragile, touched, spurious, moonstruck. dodgy, mad, insubstantial. false, delicate. weak. off. irrational
illogical.
plausible
specious.
preposterous
absurd.

Usage examples for unsound

  1. Killing by a child or a person of unsound mind shall be pardoned from the King's indictment. – Our Legal Heritage, 4th Ed. by S. A. Reilly
  2. If the visitor persists until Edison has seen both sides of the controversy, he is always willing to frankly admit that his own views may be unsound and that his opponent is right. – Edison, His Life and Inventions by Frank Lewis Dyer and Thomas Commerford Martin
  3. In Middle Florida, a broken- winded negro is more common than a broken- winded horse; though usually, when they are declared unsound or when their constitution is so broken that their recovery is despaired of, they are exported to New Orleans, to drag out the remainder of their days in the cane- field and sugar house. – The Anti-Slavery Examiner, Omnibus by American Anti-Slavery Society