adjective, un·sound·er, un·sound·est.
Examples from the Web for unsound
That could easily prove an unsound assumption, but bear with me.Yes, We Scan: Why the NSA Collected Intelligence on Mexico and France|David Frum|October 22, 2013|DAILY BEAST
In 2005, a sort of freeze was ordered, leaving the residents in the unsound status quo.
If one demolished an unsound doctrine, it was preached up again by the other.Amenities of Literature|Isaac Disraeli
But it is one thing to examine foundations, a different one to declare and prove them unsound.Mrs. Maxon Protests|Anthony Hope
On his next trip, however, Captain Vesey learned that the boy was to be returned to him as unsound and subject to epileptic fits.A Social History of The American Negro|Benjamin Brawley
The flour made from wheat so treated may be weak, but will not usually be unsound.
Selfishness is the dross and alloy that gives the unsound ring to many an act that has been called glorious.A Book of Golden Deeds|Charlotte M. Yonge
British Dictionary definitions for unsound
Word Origin and History for unsound
early 14c., of persons, "diseased, wounded," from un- (1) "not" + sound (adj.). Cf. Middle Low German unsund, Middle Dutch ongesont, German ungesund. Meaning "morally corrupt" is recorded from c.1300; that of "not mentally healthy" is from 1540s. Sense of "not based on reasoning or fact" is attested from 1590s.