Inefficient
Part of speech: adjective
Definition: Not efficient; not producing the effect intended or desired; inefficacious; as, inefficient means or measures. Incapable of, or indisposed to, effective action; habitually slack or remiss; effecting little or nothing; as, inefficient workers; an inefficient administrator.
Example sentence: You can make a lot of mistakes and still recover if you run an efficient operation. Or you can be brilliant and still go out of business if you're too inefficient.
Incompetent
Part of speech: noun
Definition: A person who is incompetent.
Part of speech: adjective
Definition: Unskilled, lacking normally expected degree of ability.Unable to make rational decisions, insane or otherwise cognitively impaired.
Example sentence: There is a power in public opinion in this country - and I thank God for it: for it is the most honest and best of all powers - which will not tolerate an incompetent or unworthy man to hold in his weak or wicked hands the lives and fortunes of his fellow-citizens.