Shady or Shaky

[matiaha]

Hey,
I will describe a situation and I would like to know what is the correct word among the 2 I'll provide to describe my feeling about the situation.
someone come up with an idea.
I didn't understand the meaning of the idea, It wasn't defined well, I asked a lot of questions to try to understand it better. while he tried to explain it to me I thought the idea could be ambiguous, undefined well.
What is the right sentence to use to describe this situation?
This is shady
OR
This is shaky

Thanks a lot!
Mati

[Josef Essberger]

Shady suggests something is borderline illegal.

Shaky suggests something is not very good and might fail.