unsound

adjective, un·sound·er, un·sound·est.

1. not sound; unhealthy, diseased, or disordered, as the body or mind.
2. decayed or impaired, as timber or foods; defective.
3. not solid or firm, as foundations.
4. not well-founded or valid; fallacious: an unsound argument.
5. easily broken; light: unsound slumber.
6. not financially strong; unreliable: an unsound corporation.

adjective

1. diseased, weak, or unstableof unsound mind
2. unreliable or fallaciousunsound advice
3. lacking solidity, strength, or firmnessunsound foundations
4. of doubtful financial or commercial viabilityan unsound enterprise
5. (of fruit, timber, etc) not in an edible or usable condition

adj.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.