unsound
un-sound
adjective
Not healthy, strong, or in good condition; defective or unreliable.
"The building's foundations were unsound."
adjective
Not based on valid reasoning or evidence; illogical or flawed.
"His entire argument was unsound."
Thesaurus
Synonyms: rotted, rotten, corroded, decayed, bad, unhealthy, unfit, wildcat, speculative, high-risk, long, risky
Antonyms: sound