The Collaborative International Dictionary of English v.0.48:

Unsound \Un*sound"\, a.
   Not sound; not whole; not solid; defective; infirm; diseased.
   [1913 Webster] -- Un*sound"ly, adv. -- Un*sound"ness, n.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

267 Moby Thesaurus words for "unsound":
   Albigensian, Arian, Catharist, Donatist, Ebionitist, Erastian,
   Gnostic, Jansenist, Jansenistic, Jovinianist, Jovinianistic,
   Lollard, Manichaean, Monophysite, Monophysitic, Montanist,
   Montanistic, Pelagian, Sabellian, Waldensian, Wyclifite, abnormal,
   adulterated, afflicted, ailing, antinomian, apocryphal, batty,
   bereft of reason, blemished, brainsick, broken-down, cachectic,
   chancy, crackbrained, cracked, crazed, crazy, crumbling, daft,
   damaged, dangerous, debilitated, decayed, decrepit, defective,
   deficient, delicate, deluded, demented, deprived of reason,
   deranged, desultory, dilapidated, diseased, disintegrating,
   disoriented, distraught, doubtful, drained, dubious, emanationist,
   enervated, erroneous, exhausted, failing, fallacious, fallible,
   faulty, feeble, flawed, flighty, flimsy, found wanting, fragile,
   frail, groundless, hairy, hallucinated, hazardous, healthless,
   heretical, heterodox, hylotheist, hylotheistic, ill, ill-advised,
   ill-considered, ill-contrived, ill-devised, ill-gauged, ill-judged,
   illogical, immature, impaired, imperfect, impolitic, imprecise,
   imprudent, impure, in poor health, inaccurate, inadequate,
   inadvisable, incomplete, inconclusive, inconsiderate, incorrect,
   indebted, indiscreet, inexact, inexpedient, infirm, injudicious,
   injured, insane, insecure, insensate, insolvent, insubstantial,
   invalid, irrational, jeopardous, lacking, languishing, loco,
   lunatic, mad, maddened, makeshift, manic, mazed, mediocre, mental,
   mentally deficient, meshuggah, mindless, misadvised, misguided,
   mixed, moon-struck, morbid, moribund, myopic, non compos,
   non compos mentis, nonorthodox, not all there, not perfect,
   not right, odd, of unsound mind, off, pale, pantheist, pantheistic,
   partial, patchy, pathological, peaked, peaky, perilous, poor,
   poorish, precarious, provisional, psycho, psychotic, queer,
   ramshackle, reasonless, reckless, reduced, reduced in health,
   rickety, risky, rocky, rotten, rotten at, run-down, senseless,
   shaky, shifting, shifty, short, shortsighted, sick, sickly,
   sketchy, slippery, specious, stark-mad, stark-staring mad, strange,
   temporary, tentative, tetched, thoughtless, ticklish, tottering,
   tottery, touched, treacherous, unaccepted, unadvised, unapproved,
   unauthentic, unauthoritative, unbalanced, uncanonical, uncertain,
   unconsidered, undependable, undeveloped, undiscerning, uneven,
   unfaithworthy, unfinished, unfirm, unforeseeing, unfounded,
   unhealthy, unhinged, unorthodox, unperfected, unpredictable,
   unproved, unreasonable, unreflecting, unreflective, unreliable,
   unrigorous, unsafe, unsane, unscriptural, unseeing, unsensible,
   unsettled, unsolid, unstable, unsteadfast, unsteady, unsturdy,
   unsubstantial, unsure, unsustained, untenable, unthinking,
   unthorough, unthoughtful, untrue, untrustworthy, unwell,
   unwholesome, unwise, valetudinarian, valetudinary, wandering, weak,
   weakened, weakly, wicked, with low resistance, witless, wobbly,
   wounded, wrong