What is the meaning behind the expression ‘Keep It Under Your Hat’?

While discretion is often considered wise, there are topics that can be risky to keep hidden—especially when it comes to mental health struggles. This is the message behind Australia’s “Don’t Keep It Under Your Hat” initiative, designed to encourage farmers to discuss their mental health challenges. But what does the phrase keep it under your hat actually mean—and where did it originate?

Brace yourself, as the true source of this phrase is still largely a mystery. However, here’s what we do know about it.

The Initial Appearances and Development of Keep It Under Your Hat

Like many words and expressions, this one has evolved, though only slightly. The earliest known uses of the phrase involved the simple expression under one’s hat, which referred to something private or hidden. As Gary Martin from Phrase Finder notes, back then, “‘under your hat’ simply meant ‘in your head.’ This meaning is evident in early written references to the phrase.” For example, in William Makepeace Thackeray’s 1848 novel History of Pendennis, the line reads: “Ah, sir—a distinct universe walks about under your hat and under mine,” and the Oxford English Dictionary’s first recorded usage is from Charlotte M. Yonge’s 1885 book Nuttie’s Father: “Nuttie ... was taking in all these revelations with an open-eyed, silent horror ... It was all under her hat, however, and the elder ladies never thought of her.”

A similar example can be found in O. Henry’s 1904 book Cabbages and Kings, where the phrase ‘under the hat’ suggests something secret or hidden: “The governor man had a bit of English under his hat, and when the music was choked off he says: ‘Ver-r-ree fine.’” Whether it referred to knowledge of a foreign language, an inconvenient opinion, or an idea kept private, anything ‘under the hat’ was something kept to oneself.

It didn’t take long for the phrase to shift to its modern meaning, “to keep something secret.” By the 1920s, examples of the phrase began to appear that would sound familiar today. For example, P.G. Wodehouse used it in 1923: “She kept it under her hat. She meant to spring it on me later, she said.” But even by 1938, Evelyn Waugh’s novel Scoop still reflected the earlier use: “Now he had something under his hat; a tip-off straight from headquarters.” Whether or not the word “keep” is included, the idiom remains as elusive as the contents of a hat.

Unclear Origins

As for where the phrase originated, etymologists have no clear answer. Some have speculated that it might relate to archers keeping their bow strings dry under their hats during rain. While archers did this, Michael Quinion of World Wide Words has debunked this theory, pointing out that the phrase is “relatively modern, centuries after the time of medieval archers or ceremonial hats.”

Quinion also examines the possibility that Abraham Lincoln inspired the phrase, as he was known for storing important documents in his stovepipe hat. However, this remains a widely debated theory—it has not been proven. Anyone claiming to know the exact origin of 'keep it under your hat' is simply making assumptions.