Source : Webster's Revised Unabridged Dictionary (1913)

Unsound \Un*sound"\, a.
   Not sound; not whole; not solid; defective; infirm; diseased.
   -- {Un*sound"ly}, adv. -- {Un*sound"ness}, n.

Source : WordNet®

unsound
     adj 1: not in good condition; damaged or decayed; "an unsound
            foundation" [ant: {sound}]
     2: not sound financially; "unsound banking practices" [ant: {sound}]
     3: containing or based on a fallacy; "fallacious reasoning";
        "an unsound argument" [syn: {fallacious}]
     4: suffering from severe mental illness; "of unsound mind"
        [syn: {mentally ill}, {unstable}]
     5: physically unsound or diseased; "has a bad back"; "a bad
        heart"; "bad teeth"; "an unsound limb"; "unsound teeth"
        [syn: {bad}, {unfit}]
     6: of e.g. advice
     7: in deplorable condition; "a street of bedraggled tenements";
        "a broken-down fence"; "a ramshackle old pier"; "a
        tumble-down shack" [syn: {bedraggled}, {broken-down}, {dilapidated},
         {ramshackle}, {tatterdemalion}, {tumble-down}]