President Donald Trump took credit in an interview for coining the phrase "prime the pump," seemingly unaware that it was popularised during the Great Depression more than 80 years ago and has been used frequently ever since.

"I came up with it a couple of days ago and I thought it was good," Mr Trump told "The Economist" magazine in an interview published on Thursday. The interviewers refrained from correcting the president about a well-worn metaphor for generating faster growth.

Those who run the Merriam-Webster dictionary quickly tweeted that the phrase "priming the pump" has been around since the early 1800s.

Literally, it's about pouring water into a pump to allow it to create suction. The phrase was commonly used by mining publications during the 1920s, but it took on new significance after the economy cratered during the Great Depression.

By 1933, President Franklin D. Roosevelt had promoted the idea of flushing money into the economy in order to stimulate stronger growth with his New Deal policies.

The notion of priming the pump is associated with the British economist John Maynard Keynes, who theorised that a government could spur a recovery from a downturn with deficit spending.