No, this isn’t a European style vacuum cleaner, but it does have a little something in common with your family’s old stand-up Hoover. It’s an adjective meaning lacking or empty of content, ideas or intelligence. In other words: stupid and boring. Remember it by picturing a vacuum cleaner sucking all of the intelligence and/or personality out of someone’s head. Many people don’t know what this means, so you can often get away with calling someone vacuous to their face, but be sure to say it with a smile and a wink, and they’ll think you’re giving them a compliment.
Example: Robert had always heard how dynamic and brilliant this famous German architect was, so imagine his supreme disappointment when, after finally meeting her in person, she came across as a vacuous bore.