Hush-hush means secret or confidential, especially when people are deliberately keeping information quiet. When a project at work is hush-hush, employees might not be allowed to talk about it, even with their families. When your parents plan a surprise party, they keep the details hush-hush so you won't find out.

The word suggests secrecy that's intentional and somewhat mysterious. A friend might whisper, “This is hush-hush, but I heard there's going to be a new principal next year.” Scientists working on breakthrough discoveries often keep their research hush-hush until they're ready to publish. Military operations are frequently hush-hush for security reasons.

The repeated “hush” comes from the sound people make when telling someone to be quiet: “Shh!” or “Hush!” So when something is hush-hush, it's as if everyone involved is constantly reminding each other not to talk about it. Unlike words like “classified” or “confidential,” which sound formal and serious, hush-hush has a lighter, almost playful tone, as if the secret might be revealed with a wink or a whisper.