I have $40000 to invest. Should i consider a 401K or a CD for maximum growth over the next 10 years?

You are talking about two different things. As Larry mentions, a 401k is a tax-deferred account that is offered through employers (self-employed people can set up an Individual 401k as well through their company). You get the benefits of being able to set aside pretty substantial amounts of you salary each year (up to $18,000 in 2015, or $24,000 if you are 50 or older) and there is often an employer match and/or a profit sharing component that may add money on top of that. With few exceptions, you will pay a penalty if you take withdrawals from a 401k prior to turning 59.5. And the return will be completely dependent on what investments you hold in the account (a one-year return in a 401k could legitimately range from -40% to +25%, though it would more likely fall somewhere in between. But again, the return will depend on what investments you hold during a given period).
A CD is basically a savings vehicle that pays you a stated interest rate for the term of the CD. CD's will generally pay a higher interest rate than a savings account, but to get that higher interest rate you have to essentially "lock up" that money for a certain period of time (for example, you can get 1-year, 2-year, 5-year CDs, as well as other lengths). In other words, if you want to pull money out of a CD before it matures, you will likely pay a penalty to do so. And the interest rates even on CDs right now are quite low (according to Bankrate, generally in the 0.50% to 2.00% range depending on the length of the CD in question).
If you are comparing only those two options (again though, they are completely different animals), I would suggest that you will get more growth through a 401k as you can invest it in a well-diversified portfolio of stocks and bonds (though if the $40,000 is just sitting there, it may be difficult, if not impossible to get it into a 401k). Even if stocks and/or bonds lag their historical returns over the next 10 years, you would be very hard pressed to get a higher annualized return from CDs over that same 10-year period.
I too would suggest meeting with a fee-only financial planner who can sit down with you and assess your entire financial picture and make suggestions on where the $40,000 should fit into that picture. For example, if you have no emergency fund set up, it might be wise to use at least a portion of the $40,000 to establish that and then look at investing the rest. If you have an emergency fund in place, and a $1,000,000 portfolio overall, then it might make sense to put the $40,000 into an individual account and invest it. Sitting down with a fee-only planner for 2-3 hours might cost a few hundred dollars, but it could be money very well spent.

Those are “apples and oranges” so let’s break it down….

First, a 401(k) is not an investment but rather a tax-deferred retirement plan. The return you receive on a 401(k) plan will depend on the investments you choose within the plan and how they perform over your 10 year period. You can only participate in a 401(k) if it’s offered through your work and you contribute through payroll deduction or you’re self-employed and you establish your own “Solo 401(k).” In 2015, you’re limited to $18,000 in contributions of earned income through payroll ($24,000 if age 50+). If you have a Solo 401(k), you can contribute more as “employer.”

A CD is a government-guaranteed (up to $250,000) savings vehicle. In the current environment, CDs pay a very low interest rate. And while it’s true that it'll pay a steady rate, the term “minimum growth” is probably more accurate than what you’re seeking.

Personally, I see a lot of headwinds over the next 7 to 10 years and expect stocks and bonds to generate very poor average annual returns from their current overpriced levels.

I’d encourage you to find a (genuine) financial planner who can help you review your broader financial picture and provide some coaching on what part this $40,000 should play in it.

I hope that helps.

SecondHalfPlanning.com