If you're a 40-year-old investor, you're probably not planning on retiring for another 20 years or more. While that may be bit of a downer for those looking forward to the freedom that retirement can bring, the positive is that it gives you more than two decades to grow your investments as you prepare for that fateful day.

Yet if you're 40 or older, your risk appetite may not be what it was back in your 20s. You want growth, but you don't want to risk losing your shirt to get it.

Fortunately, there are some businesses that, thanks to their dominant competitive advantages, offer an excellent combination of growth and relative safety. Read on to learn about three of the best.

Goog Alphabet Homescreen

Image Source: Alphabet

Alphabet (NASDAQ:GOOG) (NASDAQ:GOOGL)
Few businesses are as dominant within their respective industries as Alphabet. The parent company of Google gives investors the opportunity to profit alongside its core Internet search business that legendary investor Charlie Munger once described as having the largest competitive moat he's ever seen.

But Alphabet consists of far more than Google's highly profitable search business. From the fast-growing online video-sharing website YouTube, to the ubiquitous Android mobile operating system, to the leading Internet browser and email in Chrome and Gmail, Alphabet possesses an incredible collection of valuable assets. 

And not to be overlooked are Alphabet's "moonshot" businesses. Self-driving cars, robotics, drones, and even life extension are all areas where Alphabet is investing. In this way, Alphabet gives investors access to a venture-capital-like business spearheaded by two of the most visionary technologists alive today, in Alphabet founders Larry Page and Sergey Brin.

With so many ways to win, Alphabet is the type of business that can help form the foundation of an investor's diversified portfolio for many years to come.

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Image Source: Facebook.

Facebook (NASDAQ:FB)
Facebook is growing increasingly dominant in several important, emerging industries. Mobile advertising, messaging, and even virtual reality are all areas where the social-media king is expanding its already commanding presence.

With more than 900 million people using its mobile app on a daily basis, Facebook is extremely well positioned to profit from the migration of advertising dollars to the mobile Web. The average American adult now spends 25% of his or her media time on mobile devices, and Facebook and its properties account for over one in five minutes on mobile in the United States. In addition, the company excels at helping advertisers effectively target potential customers, thereby delivering high returns on their advertising investments. That, in turn, is fueling Facebook's torrid revenue growth, with mobile ad sales soaring 81% year over year in the most recent quarter.

Like Alphabet, Facebook owns a series of high-potential assets that add an additional element of growth to its business. Instagram (400 million users), Messenger (800 million users), and WhatsApp (nearly 1 billion users) all hold tremendous promise, and Facebook has barely begun to monetize these platforms. And with its recent acquisition of Oculus, Facebook also possesses some of the leading technology in virtual reality -- a market that's projected to explode in the years ahead.

All told, few businesses give investors a way to profit from so many powerful trends as Facebook.

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Image Source: Amazon.com.

Amazon.com (NASDAQ:AMZN)
Amazon.com has built a nearly unassailable competitive position within the online retail arena. The e-commerce juggernaut offers shoppers a value proposition -- built upon low prices, an unmatched selection of goods, inexpensive shipping, excellent customer service, and a highly convenient shopping experience -- that its competitors simply can't match.

Founder and CEO Jeff Bezos is relentless in widening Amazon's competitive moat. Whether it's expanding the company's massive global distribution system to reduce shipping times, or investing heavily to bolster the content and service offerings of Amazon's fast-growing Prime membership service, Bezos is constantly working to deliver more value to Amazon's customers. In the process, he's positioned Amazon and its shareholders to be the primary beneficiaries from the steady growth of e-commerce in the years -- and even decades -- ahead.

Incredibly, Amazon has another growth driver that may be even more powerful than its core online retail operations. Amazon Web Services has quickly become the dominant provider of scalable cloud computing services. AWS has a massive market opportunity -- so large, in fact, that Amazon's management believes it could eventually rival the company's retail operations in size. The business is already making progress in that regard, with AWS's fourth-quarter revenue surging 69% to $2.4 billion and operating income soaring 186% to $687 million. But AWS has just barely scratched the surface of its potential, and should continue to turbocharge Amazon's revenue and profit growth for many years to come.

With its formidable online retail operations and high-growth AWS business leading the way, Amazon has all the making of a multi-decade growth story, and a powerful profit opportunity for investors to consider.

Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Joe Tenebruso has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Alphabet (A shares), Alphabet (C shares), Amazon.com, and Facebook. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.