Step 1: Order
The highest derivative is \(\frac{d^3y}{dx^3}\), so the order is \(3\).
Step 2: Degree
Degree is the power of the highest derivative once the equation is a polynomial in its derivatives. Here \(\cos\left(\frac{d^2y}{dx^2}\right)\) is not a polynomial in the derivative, so it cannot be cleared.
Step 3: Result
The degree is not defined. Option (C). Options (A) and (B) assign a degree, and option (D) gives the wrong order.
Final Answer:
Order is 3 and the degree is not defined.
\[ \boxed{\text{(C)}\ \text{Order}=3,\ \text{degree not defined}} \]