It mean to be dishonest
Nick notices that Jordan Baker is incurably dishonest and often avoids taking responsibility for her actions. This flaw in her character is portrayed through her tendency to manipulate the truth and maintain a detached attitude towards moral values.
A deceitful or dishonest act
It means to be dishonest, deceitful or hypocritical.
dis-honest
Lie, untruthful, and bent.
You collect unemployment checks, but don't work.
It's a rather odd, stilted way of saying "This person may be dishonest". Out of context and at a guess, I'd say it's meant to emphasize the likelihood that the person in question is dishonest ("he's probably dishonest"), as opposed to the other way around ("he MAY be dishonest, but probably not").
Nick continues to associate with Jordan because of their physical attraction and shared social circles. He may also be drawn to her confident and assertive personality. Additionally, their relationship provides a sense of intrigue and challenge for Nick, adding excitement to his otherwise mundane life.
Deductive*
not honest. Deception, not being able to be trusted. Lying, cheating, etc.
Dishonest.